diff --git a/CHANGES.md b/CHANGES.md
index eec918f..8321f7b 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,5 +1,8 @@
 # Changes
 
+## Version 0.3.2
+- `vgsdrun` にステップ実行機能 ( `-s` オプション ) を追加
+
 ## Version 0.3.1
 - `vgsdrun` の出力結果にラベル情報を表示するように変更
 - `vgsasm` のテストを追加
diff --git a/README.md b/README.md
index 22713fa..815d0c2 100644
--- a/README.md
+++ b/README.md
@@ -282,17 +282,18 @@ negative:
 
 ## Debugger
 ### vgsdrun command
-アセンブリ言語ソース (.asm) ファイルを実際に vgs-cpu で実行した時の流れを表示
 ```
-$ vgsdrun input-source
+$ vgsdrun [-s] input-source
 ```
+- アセンブリ言語ソース (.asm) ファイルを実際に vgs-cpu で実行した時の流れを表示
+- `-s` オプションを指定すればステップ実行
 
 #### record format
 ```
 <address>: opcodes : line#<number> > assembly-source
 ```
 
-#### example
+#### example: run all
 ```
 $ ./vgsdrun src/test/asm_add_a.asm 
 assembling: src/test/asm_add_a.asm on memory
@@ -360,8 +361,32 @@ starting debug run.
 000000ff: 46 01                  : line#00070 > LD   D, 1
 00000101: 00                     : line#00071 > BRK 
 
-[registers]
+registers:
 c->r.a = 22222222, c->r.b = 11110000, c->r.c = 00001111, c->r.d = 00000001
 c->r.p = 00000101, c->r.s = 00000000, c->f.z = 00000000, c->f.q = 00000000
 $
 ```
+
+#### example: step execution
+```
+$ ./vgsdrun src/test/asm_mul.asm  -s
+assembling: src/test/asm_mul.asm on memory
+starting debug run.
+00000000: ----- start-a -----
+00000000: 08 E8 03               : line#00006 > LD   A, 1000
+00000003: 6F 64                  : line#00007 > MUL  A, 100
+00000005: A7 A0 86 01 00         : line#00008 > CMP  A, 100000
+0000000a: F8 08 03 00 00         : line#00009 > JNE  $308 (test-failed)
+> h
+command usage:
+- h     ... help
+- r     ... show registers
+- q     ... quit
+- other ... execute next line
+> r
+registers:
+c->r.a = 000186A0, c->r.b = 00000000, c->r.c = 00000000, c->r.d = 00000000
+c->r.p = 0000000A, c->r.s = 00000000, c->f.z = 00000000, c->f.q = 00000000
+> q
+$
+```
\ No newline at end of file
diff --git a/src/asm/vgsasm.c b/src/asm/vgsasm.c
index ea1ebc8..7428a36 100644
--- a/src/asm/vgsasm.c
+++ b/src/asm/vgsasm.c
@@ -19,6 +19,11 @@ static int check_arguments(int argc, char* argv[])
             if (argc <= ++i) return -1;
             if (sizeof(PT.output) <= strlen(argv[i])) return -1;
             strcpy(PT.output, argv[i]);
+#ifdef VGSDRUN
+        } else if (0 == strcmp("-s", argv[i])) {
+            if (PT.step_exec) return -1;
+            PT.step_exec = 1;
+#endif
         } else {
             if (PT.input[0]) return -1;
             if (sizeof(PT.input) <= strlen(argv[i])) return -1;
diff --git a/src/asm/vgsasm.h b/src/asm/vgsasm.h
index ad422ba..7c226bc 100644
--- a/src/asm/vgsasm.h
+++ b/src/asm/vgsasm.h
@@ -71,6 +71,7 @@ struct program_table {
     char* buffer;
     struct line_data* line;
     int line_number;
+    int step_exec;
 };
 
 char* load_file(const char* path);
diff --git a/src/asm/vgsdrun.c b/src/asm/vgsdrun.c
index 04630f1..4b1fc4d 100644
--- a/src/asm/vgsdrun.c
+++ b/src/asm/vgsdrun.c
@@ -115,13 +115,40 @@ int vgsdrun(struct program_table* pt)
     return 0;
 }
 
+static void put_registers(struct vgscpu_context* c)
+{
+    printf("registers:\n");
+    printf("c->r.a = %08X, c->r.b = %08X, c->r.c = %08X, c->r.d = %08X\n", c->r.a, c->r.b, c->r.c, c->r.d);
+    printf("c->r.p = %08X, c->r.s = %08X, c->f.z = %08X, c->f.q = %08X\n", c->r.p, c->r.s, c->f.z, c->f.z);
+}
+
 void vgsdrun_callback(struct vgscpu_context* c)
 {
     if (show_op(c->r.p)) {
         printf("invalid address: $%x\n", c->r.p);
     } else if (0x00 == c->p[c->r.p]) {
-        printf("\n[registers]\n");
-        printf("c->r.a = %08X, c->r.b = %08X, c->r.c = %08X, c->r.d = %08X\n", c->r.a, c->r.b, c->r.c, c->r.d);
-        printf("c->r.p = %08X, c->r.s = %08X, c->f.z = %08X, c->f.q = %08X\n", c->r.p, c->r.s, c->f.z, c->f.z);
+        puts("");
+        put_registers(c);
+    } else if (PT.step_exec) {
+        while (1) {
+            char buf[1024];
+            printf("> ");
+            buf[sizeof(buf) - 1] = '\0';
+            if (!fgets(buf, sizeof(buf) - 1, stdin)) return;
+            if (0 == strncmp(buf, "h", 1)) {
+                puts("command usage:");
+                puts("- h     ... help");
+                puts("- r     ... show registers");
+                puts("- q     ... quit");
+                puts("- other ... execute next line");
+            } else if (0 == strncmp(buf, "r", 1)) {
+                put_registers(c);
+            } else if (0 == strncmp(buf, "q", 1)) {
+                exit(0);
+            } else {
+                printf("\033[1A");
+                break;
+            }
+        }
     }
 }