diff --git a/build.gradle.kts b/build.gradle.kts
index bf4d22d..0c252ad 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -34,6 +34,8 @@ dependencies {
     testImplementation(group = "org.junit.jupiter", name = "junit-jupiter", version = "5.6.0") {
         exclude(group = "org.junit.vintage", module = "junit-vintage-engine")
     }
+    // https://mvnrepository.com/artifact/io.mockk/mockk
+    testImplementation("io.mockk:mockk:1.9.3")
 }
 
 tasks {
diff --git a/src/main/java/com/mapk/core/BucketGenerator.java b/src/main/java/com/mapk/core/BucketGenerator.java
new file mode 100644
index 0000000..b74eda7
--- /dev/null
+++ b/src/main/java/com/mapk/core/BucketGenerator.java
@@ -0,0 +1,50 @@
+package com.mapk.core;
+
+import kotlin.Pair;
+import kotlin.reflect.KParameter;
+
+import java.util.ArrayList;
+import java.util.List;
+
+class BucketGenerator {
+    private final int initializationStatus;
+    private final List<Integer> initializeMask;
+    private final int completionValue;
+
+    private final KParameter[] keyArray;
+    private final Object[] valueArray;
+
+    BucketGenerator(int capacity, Pair<KParameter, Object> instancePair) {
+        keyArray = new KParameter[capacity];
+        valueArray = new Object[capacity];
+
+        if (instancePair != null) {
+            initializationStatus = 1;
+
+            keyArray[0] = instancePair.getFirst();
+            valueArray[0] = instancePair.getSecond();
+        } else {
+            initializationStatus = 0;
+        }
+
+        initializeMask = new ArrayList<>(capacity);
+        int completionValue = 0;
+
+        for (int i = 0, mask = 1; i < capacity; i++, mask <<= 1) {
+            initializeMask.add(i, mask);
+            completionValue |= mask;
+        }
+
+        this.completionValue = completionValue;
+    }
+
+    ArgumentBucket generate() {
+        return new ArgumentBucket(
+                keyArray.clone(),
+                valueArray.clone(),
+                initializationStatus,
+                initializeMask,
+                completionValue
+        );
+    }
+}
diff --git a/src/main/kotlin/com/mapk/core/ArgumentBucket.kt b/src/main/kotlin/com/mapk/core/ArgumentBucket.kt
index a08c25a..d148cff 100644
--- a/src/main/kotlin/com/mapk/core/ArgumentBucket.kt
+++ b/src/main/kotlin/com/mapk/core/ArgumentBucket.kt
@@ -2,47 +2,60 @@ package com.mapk.core
 
 import kotlin.reflect.KParameter
 
-internal class BucketGenerator(
-    private val bucket: Array<Any?>,
-    private val instancePair: Pair<KParameter, Any?>?,
-    private val initializationStatus: Int,
-    private val initializeMask: List<Int>
-) {
-    private val completionValue: Int = initializeMask.reduce { l, r -> l or r }
-    private val bucketSize = bucket.size
-
-    fun generate(): ArgumentBucket {
-        val tempMap = HashMap<KParameter, Any?>(bucketSize, 1.0f)
-        instancePair?.run { tempMap[this.first] = this.second }
-
-        return ArgumentBucket(
-            bucket.copyOf(),
-            tempMap,
-            initializationStatus,
-            initializeMask,
-            completionValue
-        )
-    }
-}
-
 class ArgumentBucket internal constructor(
-    internal val bucket: Array<Any?>,
-    internal val bucketMap: MutableMap<KParameter, Any?>,
+    private val keyArray: Array<KParameter?>,
+    internal val valueArray: Array<Any?>,
     private var initializationStatus: Int,
     private val initializeMask: List<Int>,
     private val completionValue: Int
-) {
+) : Map<KParameter, Any?> {
+    // インスタンス有りなら1、そうでなければ0スタート
+    private var count: Int = initializationStatus
+
     val isInitialized: Boolean get() = initializationStatus == completionValue
 
-    fun setArgument(kParameter: KParameter, argument: Any?) {
-        val index = kParameter.index
+    class MutableEntry internal constructor(
+        override val key: KParameter,
+        override var value: Any?
+    ) : Map.Entry<KParameter, Any?>
+
+    override val size: Int get() = count
+
+    override fun containsKey(key: KParameter): Boolean {
+        // NOTE: もしかしたらステータスを見た方が速いかも
+        return keyArray[key.index] != null
+    }
+
+    override fun containsValue(value: Any?): Boolean {
+        throw UnsupportedOperationException()
+    }
+
+    override fun get(key: KParameter): Any? = valueArray[key.index]
+    fun getByIndex(key: Int): Any? =
+        if (initializationStatus and initializeMask[key] != 0) valueArray[key]
+        else throw IllegalStateException("This argument is not initialized.")
+
+    override fun isEmpty(): Boolean = count == 0
+
+    override val entries: Set<Map.Entry<KParameter, Any?>>
+        get() = keyArray.mapNotNull { it?.let { MutableEntry(it, valueArray[it.index]) } }.toSet()
+    override val keys: MutableSet<KParameter>
+        get() = keyArray.filterNotNull().toMutableSet()
+    override val values: MutableCollection<Any?>
+        get() = throw UnsupportedOperationException()
+
+    fun putIfAbsent(key: KParameter, value: Any?) {
+        val index = key.index
         val temp = initializationStatus or initializeMask[index]
 
         // 先に入ったものを優先するため、初期化済みなら何もしない
         if (initializationStatus == temp) return
 
-        bucketMap[kParameter] = argument
-        bucket[index] = argument
+        count += 1
         initializationStatus = temp
+        keyArray[index] = key
+        valueArray[index] = value
+
+        return
     }
 }
diff --git a/src/main/kotlin/com/mapk/core/KFunctionForCall.kt b/src/main/kotlin/com/mapk/core/KFunctionForCall.kt
index 47cc3e4..33b8a3f 100644
--- a/src/main/kotlin/com/mapk/core/KFunctionForCall.kt
+++ b/src/main/kotlin/com/mapk/core/KFunctionForCall.kt
@@ -15,23 +15,16 @@ class KFunctionForCall<T>(private val function: KFunction<T>, instance: Any? = n
         // この関数には確実にアクセスするためアクセシビリティ書き換え
         function.isAccessible = true
 
-        // 初期化処理の共通化のため先に初期化
-        val tempArray = Array<Any?>(parameters.size) { null }
-        val maskList = generateSequence(1) { it.shl(1) }.take(parameters.size).toList()
-
         generator = if (instance != null) {
-            tempArray[0] = instance
-
-            // 引数の1番目は初期化済みということでinitializationStatusは1スタート
-            BucketGenerator(tempArray, parameters.first { it.kind == KParameter.Kind.INSTANCE } to instance, 1, maskList)
+            BucketGenerator(parameters.size, parameters.first { it.kind == KParameter.Kind.INSTANCE } to instance)
         } else {
-            BucketGenerator(tempArray, null, 0, maskList)
+            BucketGenerator(parameters.size, null)
         }
     }
 
     fun getArgumentBucket(): ArgumentBucket = generator.generate()
 
     fun call(argumentBucket: ArgumentBucket): T =
-        if (argumentBucket.isInitialized) function.call(*argumentBucket.bucket)
-        else function.callBy(argumentBucket.bucketMap)
+        if (argumentBucket.isInitialized) function.call(*argumentBucket.valueArray)
+        else function.callBy(argumentBucket)
 }
diff --git a/src/test/kotlin/com/mapk/core/ArgumentBucketTest.kt b/src/test/kotlin/com/mapk/core/ArgumentBucketTest.kt
index 02561c2..c9f820c 100644
--- a/src/test/kotlin/com/mapk/core/ArgumentBucketTest.kt
+++ b/src/test/kotlin/com/mapk/core/ArgumentBucketTest.kt
@@ -36,7 +36,7 @@ class ArgumentBucketTest {
         @DisplayName("初期化後")
         fun isInitialized() {
             ::sampleFunction.parameters.forEach {
-                argumentBucket.setArgument(it, object {})
+                argumentBucket.putIfAbsent(it, object {})
             }
 
             assertTrue(argumentBucket.isInitialized)
@@ -50,8 +50,8 @@ class ArgumentBucketTest {
         @DisplayName("正常に追加した場合")
         fun setNewArgument() {
             val parameter = ::sampleFunction.parameters.first { it.index == 0 }
-            argumentBucket.setArgument(parameter, "argument")
-            assertEquals("argument", argumentBucket.bucket[0])
+            argumentBucket.putIfAbsent(parameter, "argument")
+            assertEquals("argument", argumentBucket.getByIndex(0))
         }
 
         @Test
@@ -59,9 +59,9 @@ class ArgumentBucketTest {
         fun setArgumentTwice() {
             val parameter = ::sampleFunction.parameters.first { it.index == 0 }
 
-            argumentBucket.setArgument(parameter, "first")
-            argumentBucket.setArgument(parameter, "second")
-            assertEquals("first", argumentBucket.bucket[0])
+            argumentBucket.putIfAbsent(parameter, "first")
+            argumentBucket.putIfAbsent(parameter, "second")
+            assertEquals("first", argumentBucket.getByIndex(0))
         }
     }
 }
diff --git a/src/test/kotlin/com/mapk/core/KFunctionForCallTest.kt b/src/test/kotlin/com/mapk/core/KFunctionForCallTest.kt
index 99d2691..daf33ea 100644
--- a/src/test/kotlin/com/mapk/core/KFunctionForCallTest.kt
+++ b/src/test/kotlin/com/mapk/core/KFunctionForCallTest.kt
@@ -1,5 +1,7 @@
 package com.mapk.core
 
+import io.mockk.spyk
+import io.mockk.verify
 import kotlin.reflect.full.functions
 import org.junit.jupiter.api.Assertions.assertEquals
 import org.junit.jupiter.api.DisplayName
@@ -42,15 +44,17 @@ class KFunctionForCallTest {
         @Test
         @DisplayName("コンパニオンオブジェクトから取得した場合")
         fun fromCompanionObject() {
-            val function =
-                Companion::class.functions.find { it.name == (KFunctionForCallTest)::declaredOnCompanionObject.name }!!
+            val function = Companion::class.functions
+                .first { it.name == (KFunctionForCallTest)::declaredOnCompanionObject.name }
+                .let { spyk(it) }
 
             val kFunctionForCall = KFunctionForCall(function, Companion)
 
             val bucket = kFunctionForCall.getArgumentBucket()
-            kFunctionForCall.parameters.forEach { bucket.setArgument(it, it.index) }
+            kFunctionForCall.parameters.forEach { bucket.putIfAbsent(it, it.index) }
             val result = kFunctionForCall.call(bucket)
             assertEquals("12", result)
+            verify(exactly = 1) { function.call(*anyVararg()) }
         }
 
         private fun func(key: String, value: String = "default"): Pair<String, String> = key to value
@@ -58,13 +62,37 @@ class KFunctionForCallTest {
         @Test
         @DisplayName("デフォルト値を用いる場合")
         fun useDefaultValue() {
-            val kFunctionForCall = KFunctionForCall(::func)
+            val func = spyk(::func)
+            val kFunctionForCall = KFunctionForCall(func)
             val argumentBucket = kFunctionForCall.getArgumentBucket()
 
-            ::func.parameters.forEach { if (!it.isOptional) argumentBucket.setArgument(it, it.name) }
+            func.parameters.forEach { if (!it.isOptional) argumentBucket.putIfAbsent(it, it.name) }
 
             val result = kFunctionForCall.call(argumentBucket)
             assertEquals("key" to "default", result)
+            verify(exactly = 1) { func.callBy(any()) }
+        }
+
+        @Test
+        @DisplayName("同一関数を違うソースから複数回呼んだ場合")
+        fun multipleCall() {
+            val function = Companion::class.functions
+                .first { it.name == (KFunctionForCallTest)::declaredOnCompanionObject.name }
+                .let { spyk(it) }
+
+            val kFunctionForCall = KFunctionForCall(function, Companion)
+
+            val bucket1 = kFunctionForCall.getArgumentBucket()
+            kFunctionForCall.parameters.forEach { bucket1.putIfAbsent(it, it.index) }
+            val result1 = kFunctionForCall.call(bucket1)
+            assertEquals("12", result1)
+
+            val bucket2 = kFunctionForCall.getArgumentBucket()
+            kFunctionForCall.parameters.forEach { bucket2.putIfAbsent(it, it.index + 1) }
+            val result2 = kFunctionForCall.call(bucket2)
+            assertEquals("23", result2)
+
+            verify(exactly = 2) { function.call(*anyVararg()) }
         }
     }