diff --git a/README.md b/README.md
index 656c64d..e934d42 100644
--- a/README.md
+++ b/README.md
@@ -14,7 +14,7 @@ To install from npm:
 $ npm install --save @fav/type.is-plain-object
 ```
 
-***NOTE:*** *npm < 2.7.0 does not support scoped package, but even old version Node.js supports it. So when you use such older npm, you should download this package from [github.com][repo-url], and move it in `node_modules/@fav/type.is-plain-object/` direcotry manually.*
+***NOTE:*** *npm < 2.7.0 does not support scoped package, but even old version Node.js supports it. So when you use such older npm, you should download this package from [github.com][repo-url], and move it in `node_modules/@fav/type.is-plain-object/` directory manually.*
 
 
 ## Usage
@@ -24,6 +24,7 @@ For Node.js, when installing `@fav/type.is-plain-object` from npm:
 ```js
 var isPlainObject = require('@fav/type.is-plain-object');
 isPlainObject({ a: 1 }); // => true
+isPlainObject.not({ a: 1 }); // => false
 ```
 
 For Web browsers:
@@ -33,6 +34,7 @@ For Web browsers:
 <script>
 var isPlainObject = fav.type.isPlainObject;
 isPlainObject({ a: 1 }); // => true
+isPlainObject.not({ a: 1 }); // => false
 </script>
 ```
 
@@ -56,6 +58,25 @@ True, if *value* is a plain object.
 **Type:** boolean
 
 
+### <u>isPlainObject.not(value) : boolean</u>
+
+Checks if *value* is not a plain object.
+
+This function always returns a negative boolean of `isPlainObject(value)`.
+
+#### Parameter:
+
+| Parameter |  Type  | Description              |
+|-----------|:------:|--------------------------|
+| value     | *any*  | The value to be checked. |
+
+#### Return:
+
+True, if *value* is not a plain object.
+
+**Type:** boolean
+
+
 ## Checked                                                                      
 
 ### Node.js (4〜8)
diff --git a/index.js b/index.js
index 7d6780f..5ef656f 100644
--- a/index.js
+++ b/index.js
@@ -22,4 +22,13 @@ function isPlainObject(value) {
   }
 }
 
+function isNotPlainObject(value) {
+  return !isPlainObject(value);
+}
+
+Object.defineProperty(isPlainObject, 'not', {
+  enumerable: true,
+  value: isNotPlainObject,
+});
+
 module.exports = isPlainObject;
diff --git a/test/is-plain-object-not.test.js b/test/is-plain-object-not.test.js
new file mode 100644
index 0000000..4724086
--- /dev/null
+++ b/test/is-plain-object-not.test.js
@@ -0,0 +1,187 @@
+'use strict';
+
+var chai = require('chai');
+var expect = chai.expect;
+var semver = require('semver');
+var fav = {}; fav.type = {}; fav.type.isPlainObject = require('..');
+
+var isNotPlainObject = fav.type.isPlainObject.not;
+
+describe('fav.type.isPlainObject.not', function() {
+
+  it('Should return false when value is a plain object', function() {
+    expect(isNotPlainObject({})).to.equal(false);
+    expect(isNotPlainObject({ a: 1 })).to.equal(false);
+    expect(isNotPlainObject(new Object())).to.equal(false);
+    expect(isNotPlainObject(Object.create(Object.prototype))).to.equal(false);
+    expect(isNotPlainObject(Object.create(null))).to.equal(false);
+  });
+
+  it('Should return true when value is not a plain object', function() {
+    expect(isNotPlainObject(undefined)).to.equal(true);
+    expect(isNotPlainObject(null)).to.equal(true);
+    expect(isNotPlainObject(true)).to.equal(true);
+    expect(isNotPlainObject(false)).to.equal(true);
+    expect(isNotPlainObject(0)).to.equal(true);
+    expect(isNotPlainObject(123)).to.equal(true);
+    expect(isNotPlainObject(NaN)).to.equal(true);
+    expect(isNotPlainObject(Infinity)).to.equal(true);
+    expect(isNotPlainObject(new Number(123))).to.equal(true);
+    expect(isNotPlainObject([])).to.equal(true);
+    expect(isNotPlainObject([1, 2])).to.equal(true);
+    expect(isNotPlainObject(new Array(1, 2))).to.equal(true);
+    expect(isNotPlainObject(/a/g)).to.equal(true);
+    expect(isNotPlainObject(new RegExp('a', 'g'))).to.equal(true);
+    expect(isNotPlainObject(function() {})).to.equal(true);
+    expect(isNotPlainObject(new Date())).to.equal(true);
+    expect(isNotPlainObject(new Error())).to.equal(true);
+    expect(isNotPlainObject(new Foo())).to.equal(true);
+    expect(isNotPlainObject(new FooEx())).to.equal(true);
+    expect(isNotPlainObject(new SubclassOfPlainObject())).to.equal(true);
+    expect(isNotPlainObject(Object.create({}))).to.equal(true);
+  });
+
+  it('Should return true when value is a class instance', function() {
+    if (!isSupportClass()) {
+      this.skip();
+      return;
+    }
+
+    var code = codeForClass();
+    eval(code);
+  });
+
+  it('Should return true when value is a symbol', function() {
+    if (typeof Symbol !== 'function') {
+      this.skip();
+      return;
+    }
+
+    expect(isNotPlainObject(Symbol('foo'))).to.equal(true);
+  });
+
+});
+
+
+function Foo() {
+  this.baz = 'Baz';
+  return this;
+}
+
+function FooEx() {
+  this.baz = 'Baaaaz';
+}
+FooEx.prototype = Foo.prototype;
+
+Foo.prototype.bar = function() {
+  return this.baz;
+};
+
+/*
+var foo = new Foo();
+console.log(foo);
+console.log(foo.baz);
+console.log(foo.bar());
+console.log(typeof foo);
+console.log(Object.prototype.toString.call(foo));
+console.log(foo.constructor);
+console.log(foo.constructor.name);
+console.log(foo.prototype);
+console.log(Object.getPrototypeOf(foo));
+console.log(foo.constructor === Object);
+
+var fooex = new FooEx();
+console.log(fooex);
+console.log(fooex.baz);
+console.log(fooex.bar());
+console.log(fooex.constructor === Object);
+*/
+
+function SubclassOfPlainObject() {}
+SubclassOfPlainObject.prototype = {};
+
+function codeForClass() {
+  return "\
+class Qux {\
+  constructor(n) {\
+    this.count = n || 1;\
+  }\
+\
+  get text() {\
+    return 'Q' + 'u'.repeat(this.count) + 'x';\
+  }\
+}\
+\
+class Quux extends Qux {\
+  constructor(n) {\
+    super(n);\
+  }\
+\
+  get text() {\
+    return 'Q' + 'u'.repeat(this.count * 2) + 'x';\
+  }\
+}\
+\
+/*\
+const qux = new Qux(3);\
+console.log(qux);\
+console.log(qux.count);\
+console.log(qux.text);\
+console.log(qux.constructor === Object);\
+*/\
+\
+/*\
+const quux = new Quux(3);\
+console.log(quux);\
+console.log(quux.count);\
+console.log(quux.text);\
+console.log(quux.constructor === Object);\
+*/\
+\
+expect(isNotPlainObject(new Qux())).to.equal(true);\
+expect(isNotPlainObject(new Quux())).to.equal(true);\
+";
+}
+
+function isSupportClass() {
+  if (isNode()) {
+    return semver.gte(process.version, '2.0.0');
+  }
+
+  if (typeof xslet !== 'undefined' && typeof xslet.platform !== 'undefined') {
+    var ua = xslet.platform.ua;
+
+    // Check by latest version
+    if (ua.CHROME) {
+      return true;
+    }
+    if (ua.FIREFOX) {
+      return true;
+    }
+    if (ua.MSIE) {
+      return false;
+    }
+    if (ua.EDGE) {
+      return true;
+    }
+    if (ua.SAFARI) {
+      return true;
+    }
+    if (ua.VIVALDI) {
+      return true;
+    }
+    if (ua.PHANTOMJS) {
+      return false;
+    }
+    return false;
+  }
+}
+
+function isNode() {
+  if (typeof process === 'object') {
+    if (typeof process.kill === 'function') { // exist from v0.0.6
+      return true;
+    }
+  }
+  return false;
+}
diff --git a/test/web/browser-test.js b/test/web/browser-test.js
index 6fdfda0..50870f0 100644
--- a/test/web/browser-test.js
+++ b/test/web/browser-test.js
@@ -6,6 +6,196 @@ var expect = chai.expect;
 
 
 
+var isNotPlainObject = fav.type.isPlainObject.not;
+
+describe('fav.type.isPlainObject.not', function() {
+
+  it('Should return false when value is a plain object', function() {
+    expect(isNotPlainObject({})).to.equal(false);
+    expect(isNotPlainObject({ a: 1 })).to.equal(false);
+    expect(isNotPlainObject(new Object())).to.equal(false);
+    expect(isNotPlainObject(Object.create(Object.prototype))).to.equal(false);
+    expect(isNotPlainObject(Object.create(null))).to.equal(false);
+  });
+
+  it('Should return true when value is not a plain object', function() {
+    expect(isNotPlainObject(undefined)).to.equal(true);
+    expect(isNotPlainObject(null)).to.equal(true);
+    expect(isNotPlainObject(true)).to.equal(true);
+    expect(isNotPlainObject(false)).to.equal(true);
+    expect(isNotPlainObject(0)).to.equal(true);
+    expect(isNotPlainObject(123)).to.equal(true);
+    expect(isNotPlainObject(NaN)).to.equal(true);
+    expect(isNotPlainObject(Infinity)).to.equal(true);
+    expect(isNotPlainObject(new Number(123))).to.equal(true);
+    expect(isNotPlainObject([])).to.equal(true);
+    expect(isNotPlainObject([1, 2])).to.equal(true);
+    expect(isNotPlainObject(new Array(1, 2))).to.equal(true);
+    expect(isNotPlainObject(/a/g)).to.equal(true);
+    expect(isNotPlainObject(new RegExp('a', 'g'))).to.equal(true);
+    expect(isNotPlainObject(function() {})).to.equal(true);
+    expect(isNotPlainObject(new Date())).to.equal(true);
+    expect(isNotPlainObject(new Error())).to.equal(true);
+    expect(isNotPlainObject(new Foo())).to.equal(true);
+    expect(isNotPlainObject(new FooEx())).to.equal(true);
+    expect(isNotPlainObject(new SubclassOfPlainObject())).to.equal(true);
+    expect(isNotPlainObject(Object.create({}))).to.equal(true);
+  });
+
+  it('Should return true when value is a class instance', function() {
+    if (!isSupportClass()) {
+      this.skip();
+      return;
+    }
+
+    var code = codeForClass();
+    eval(code);
+  });
+
+  it('Should return true when value is a symbol', function() {
+    if (typeof Symbol !== 'function') {
+      this.skip();
+      return;
+    }
+
+    expect(isNotPlainObject(Symbol('foo'))).to.equal(true);
+  });
+
+});
+
+
+function Foo() {
+  this.baz = 'Baz';
+  return this;
+}
+
+function FooEx() {
+  this.baz = 'Baaaaz';
+}
+FooEx.prototype = Foo.prototype;
+
+Foo.prototype.bar = function() {
+  return this.baz;
+};
+
+/*
+var foo = new Foo();
+console.log(foo);
+console.log(foo.baz);
+console.log(foo.bar());
+console.log(typeof foo);
+console.log(Object.prototype.toString.call(foo));
+console.log(foo.constructor);
+console.log(foo.constructor.name);
+console.log(foo.prototype);
+console.log(Object.getPrototypeOf(foo));
+console.log(foo.constructor === Object);
+
+var fooex = new FooEx();
+console.log(fooex);
+console.log(fooex.baz);
+console.log(fooex.bar());
+console.log(fooex.constructor === Object);
+*/
+
+function SubclassOfPlainObject() {}
+SubclassOfPlainObject.prototype = {};
+
+function codeForClass() {
+  return "\
+class Qux {\
+  constructor(n) {\
+    this.count = n || 1;\
+  }\
+\
+  get text() {\
+    return 'Q' + 'u'.repeat(this.count) + 'x';\
+  }\
+}\
+\
+class Quux extends Qux {\
+  constructor(n) {\
+    super(n);\
+  }\
+\
+  get text() {\
+    return 'Q' + 'u'.repeat(this.count * 2) + 'x';\
+  }\
+}\
+\
+/*\
+const qux = new Qux(3);\
+console.log(qux);\
+console.log(qux.count);\
+console.log(qux.text);\
+console.log(qux.constructor === Object);\
+*/\
+\
+/*\
+const quux = new Quux(3);\
+console.log(quux);\
+console.log(quux.count);\
+console.log(quux.text);\
+console.log(quux.constructor === Object);\
+*/\
+\
+expect(isNotPlainObject(new Qux())).to.equal(true);\
+expect(isNotPlainObject(new Quux())).to.equal(true);\
+";
+}
+
+function isSupportClass() {
+  if (isNode()) {
+    return semver.gte(process.version, '2.0.0');
+  }
+
+  if (typeof xslet !== 'undefined' && typeof xslet.platform !== 'undefined') {
+    var ua = xslet.platform.ua;
+
+    // Check by latest version
+    if (ua.CHROME) {
+      return true;
+    }
+    if (ua.FIREFOX) {
+      return true;
+    }
+    if (ua.MSIE) {
+      return false;
+    }
+    if (ua.EDGE) {
+      return true;
+    }
+    if (ua.SAFARI) {
+      return true;
+    }
+    if (ua.VIVALDI) {
+      return true;
+    }
+    if (ua.PHANTOMJS) {
+      return false;
+    }
+    return false;
+  }
+}
+
+function isNode() {
+  if (typeof process === 'object') {
+    if (typeof process.kill === 'function') { // exist from v0.0.6
+      return true;
+    }
+  }
+  return false;
+}
+
+})();
+(function(){
+'use strict';
+
+
+var expect = chai.expect;
+
+
+
 var isPlainObject = fav.type.isPlainObject;
 
 describe('fav.type.isPlainObject', function() {
diff --git a/web/fav.type.is-plain-object.js b/web/fav.type.is-plain-object.js
index 939e897..7ace4ae 100644
--- a/web/fav.type.is-plain-object.js
+++ b/web/fav.type.is-plain-object.js
@@ -23,6 +23,15 @@ function isPlainObject(value) {
   }
 }
 
+function isNotPlainObject(value) {
+  return !isPlainObject(value);
+}
+
+Object.defineProperty(isPlainObject, 'not', {
+  enumerable: true,
+  value: isNotPlainObject,
+});
+
 module.exports = isPlainObject;
 
 },{}]},{},[1])(1)
diff --git a/web/fav.type.is-plain-object.min.js b/web/fav.type.is-plain-object.min.js
index 5814d15..ff14599 100644
--- a/web/fav.type.is-plain-object.min.js
+++ b/web/fav.type.is-plain-object.min.js
@@ -1,2 +1,2 @@
-!function(e){if("object"==typeof exports&&"undefined"!=typeof module)module.exports=e();else if("function"==typeof define&&define.amd)define([],e);else{var t;(t=(t=(t="undefined"!=typeof window?window:"undefined"!=typeof global?global:"undefined"!=typeof self?self:this).fav||(t.fav={})).type||(t.type={})).isPlainObject=e()}}(function(){return function e(t,n,r){function o(i,u){if(!n[i]){if(!t[i]){var c="function"==typeof require&&require;if(!u&&c)return c(i,!0);if(f)return f(i,!0);var p=new Error("Cannot find module '"+i+"'");throw p.code="MODULE_NOT_FOUND",p}var d=n[i]={exports:{}};t[i][0].call(d.exports,function(e){var n=t[i][1][e];return o(n||e)},d,d.exports,e,t,n,r)}return n[i].exports}for(var f="function"==typeof require&&require,i=0;i<r.length;i++)o(r[i]);return o}({1:[function(e,t,n){"use strict";t.exports=function(e){if("object"!=typeof e)return!1;if("[object Object]"!==Object.prototype.toString.call(e))return!1;switch(Object.getPrototypeOf(e)){case Object.prototype:case null:return!0;default:return!1}}},{}]},{},[1])(1)});
+!function(e){if("object"==typeof exports&&"undefined"!=typeof module)module.exports=e();else if("function"==typeof define&&define.amd)define([],e);else{var t;(t=(t=(t="undefined"!=typeof window?window:"undefined"!=typeof global?global:"undefined"!=typeof self?self:this).fav||(t.fav={})).type||(t.type={})).isPlainObject=e()}}(function(){return function e(t,n,r){function o(i,u){if(!n[i]){if(!t[i]){var c="function"==typeof require&&require;if(!u&&c)return c(i,!0);if(f)return f(i,!0);var p=new Error("Cannot find module '"+i+"'");throw p.code="MODULE_NOT_FOUND",p}var l=n[i]={exports:{}};t[i][0].call(l.exports,function(e){var n=t[i][1][e];return o(n||e)},l,l.exports,e,t,n,r)}return n[i].exports}for(var f="function"==typeof require&&require,i=0;i<r.length;i++)o(r[i]);return o}({1:[function(e,t,n){"use strict";function r(e){if("object"!=typeof e)return!1;if("[object Object]"!==Object.prototype.toString.call(e))return!1;switch(Object.getPrototypeOf(e)){case Object.prototype:case null:return!0;default:return!1}}Object.defineProperty(r,"not",{enumerable:!0,value:function(e){return!r(e)}}),t.exports=r},{}]},{},[1])(1)});
 //# sourceMappingURL=fav.type.is-plain-object.min.js.map
\ No newline at end of file
diff --git a/web/fav.type.is-plain-object.min.js.map b/web/fav.type.is-plain-object.min.js.map
index 7b226b6..58cdc93 100644
--- a/web/fav.type.is-plain-object.min.js.map
+++ b/web/fav.type.is-plain-object.min.js.map
@@ -1 +1 @@
-{"version":3,"sources":["fav.type.is-plain-object.js"],"names":["f","exports","module","define","amd","g","window","global","self","this","fav","type","isPlainObject","e","t","n","r","s","o","u","a","require","i","Error","code","l","call","length","1","value","Object","prototype","toString","getPrototypeOf"],"mappings":"CAAA,SAAUA,GAAG,GAAoB,iBAAVC,SAAoC,oBAATC,OAAsBA,OAAOD,QAAQD,SAAS,GAAmB,mBAATG,QAAqBA,OAAOC,IAAKD,UAAUH,OAAO,CAAC,IAAIK,GAAuKA,GAAxBA,GAA7GA,EAAb,oBAATC,OAAwBA,OAA+B,oBAATC,OAAwBA,OAA6B,oBAAPC,KAAsBA,KAAYC,MAAUC,MAAML,EAAEK,SAAgBC,OAAON,EAAEM,UAAcC,cAAgBZ,KAApX,CAA2X,WAAqC,OAAO,SAAUa,EAAEC,EAAEC,EAAEC,GAAG,SAASC,EAAEC,EAAEC,GAAG,IAAIJ,EAAEG,GAAG,CAAC,IAAIJ,EAAEI,GAAG,CAAC,IAAIE,EAAkB,mBAATC,SAAqBA,QAAQ,IAAIF,GAAGC,EAAE,OAAOA,EAAEF,GAAE,GAAI,GAAGI,EAAE,OAAOA,EAAEJ,GAAE,GAAI,IAAIlB,EAAE,IAAIuB,MAAM,uBAAuBL,EAAE,KAAK,MAAMlB,EAAEwB,KAAK,mBAAmBxB,EAAE,IAAIyB,EAAEV,EAAEG,IAAIjB,YAAYa,EAAEI,GAAG,GAAGQ,KAAKD,EAAExB,QAAQ,SAASY,GAAG,IAAIE,EAAED,EAAEI,GAAG,GAAGL,GAAG,OAAOI,EAAEF,GAAIF,IAAIY,EAAEA,EAAExB,QAAQY,EAAEC,EAAEC,EAAEC,GAAG,OAAOD,EAAEG,GAAGjB,QAAkD,IAAI,IAA1CqB,EAAkB,mBAATD,SAAqBA,QAAgBH,EAAE,EAAEA,EAAEF,EAAEW,OAAOT,IAAID,EAAED,EAAEE,IAAI,OAAOD,EAAvb,EAA4bW,GAAG,SAASP,EAAQnB,EAAOD,GAC93B,aAwBAC,EAAOD,QAtBP,SAAuB4B,GACrB,GAAqB,iBAAVA,EACT,OAAO,EAGT,GAA8C,oBAA1CC,OAAOC,UAAUC,SAASN,KAAKG,GACjC,OAAO,EAGT,OAAQC,OAAOG,eAAeJ,IAC5B,KAAKC,OAAOC,UAGZ,KAAK,KACH,OAAO,EAET,QACE,OAAO,cAOF,GA3B4Z,CA2BxZ"}
\ No newline at end of file
+{"version":3,"sources":["fav.type.is-plain-object.js"],"names":["f","exports","module","define","amd","g","window","global","self","this","fav","type","isPlainObject","e","t","n","r","s","o","u","a","require","i","Error","code","l","call","length","1","value","Object","prototype","toString","getPrototypeOf","defineProperty","enumerable"],"mappings":"CAAA,SAAUA,GAAG,GAAoB,iBAAVC,SAAoC,oBAATC,OAAsBA,OAAOD,QAAQD,SAAS,GAAmB,mBAATG,QAAqBA,OAAOC,IAAKD,UAAUH,OAAO,CAAC,IAAIK,GAAuKA,GAAxBA,GAA7GA,EAAb,oBAATC,OAAwBA,OAA+B,oBAATC,OAAwBA,OAA6B,oBAAPC,KAAsBA,KAAYC,MAAUC,MAAML,EAAEK,SAAgBC,OAAON,EAAEM,UAAcC,cAAgBZ,KAApX,CAA2X,WAAqC,OAAO,SAAUa,EAAEC,EAAEC,EAAEC,GAAG,SAASC,EAAEC,EAAEC,GAAG,IAAIJ,EAAEG,GAAG,CAAC,IAAIJ,EAAEI,GAAG,CAAC,IAAIE,EAAkB,mBAATC,SAAqBA,QAAQ,IAAIF,GAAGC,EAAE,OAAOA,EAAEF,GAAE,GAAI,GAAGI,EAAE,OAAOA,EAAEJ,GAAE,GAAI,IAAIlB,EAAE,IAAIuB,MAAM,uBAAuBL,EAAE,KAAK,MAAMlB,EAAEwB,KAAK,mBAAmBxB,EAAE,IAAIyB,EAAEV,EAAEG,IAAIjB,YAAYa,EAAEI,GAAG,GAAGQ,KAAKD,EAAExB,QAAQ,SAASY,GAAG,IAAIE,EAAED,EAAEI,GAAG,GAAGL,GAAG,OAAOI,EAAEF,GAAIF,IAAIY,EAAEA,EAAExB,QAAQY,EAAEC,EAAEC,EAAEC,GAAG,OAAOD,EAAEG,GAAGjB,QAAkD,IAAI,IAA1CqB,EAAkB,mBAATD,SAAqBA,QAAgBH,EAAE,EAAEA,EAAEF,EAAEW,OAAOT,IAAID,EAAED,EAAEE,IAAI,OAAOD,EAAvb,EAA4bW,GAAG,SAASP,EAAQnB,EAAOD,GAC93B,aAEA,SAASW,EAAciB,GACrB,GAAqB,iBAAVA,EACT,OAAO,EAGT,GAA8C,oBAA1CC,OAAOC,UAAUC,SAASN,KAAKG,GACjC,OAAO,EAGT,OAAQC,OAAOG,eAAeJ,IAC5B,KAAKC,OAAOC,UAGZ,KAAK,KACH,OAAO,EAET,QACE,OAAO,GASbD,OAAOI,eAAetB,EAAe,OACnCuB,YAAY,EACZN,MANF,SAA0BA,GACxB,OAAQjB,EAAciB,MAQxB3B,EAAOD,QAAUW,YAEN,GApC4Z,CAoCxZ"}
\ No newline at end of file