diff --git a/himu/assets/js/app.js b/himu/assets/js/app.js
index 9bd3ef5..f5978be 100644
--- a/himu/assets/js/app.js
+++ b/himu/assets/js/app.js
@@ -115,7 +115,7 @@
             const index = this.messages.findIndex(m => {
               return m.id === updatedMessage.id
             })
-            Vue.set(this.messages, index, updatedMessage)
+            Vue.set(this.messages, index, response.result)
         })
       },
       clearMessage() {
diff --git a/himu/controller/message.go b/himu/controller/message.go
index 0e54c5f..3f0cf8b 100644
--- a/himu/controller/message.go
+++ b/himu/controller/message.go
@@ -98,8 +98,42 @@ func (m *Message) Create(c *gin.Context) {
 // UpdateByID は...
 func (m *Message) UpdateByID(c *gin.Context) {
 	// Mission 1-1. メッセージを編集しよう
-	// ...
-	c.JSON(http.StatusCreated, gin.H{})
+
+	msg, err := model.MessageByID(m.DB, c.Param("id"))
+	switch {
+	case err == sql.ErrNoRows:
+		resp := httputil.NewErrorResponse(err)
+		c.JSON(http.StatusNotFound, resp)
+		return
+	case err != nil:
+		resp := httputil.NewErrorResponse(err)
+		c.JSON(http.StatusInternalServerError, resp)
+		return
+	}
+
+	var requestMessage model.Message
+	if c.Request.ContentLength == 0 {
+		resp := httputil.NewErrorResponse(errors.New("body is missing"))
+		c.JSON(http.StatusBadRequest, resp)
+		return
+	}
+	if err := c.BindJSON(&requestMessage); err != nil {
+		resp := httputil.NewErrorResponse(err)
+		c.JSON(http.StatusInternalServerError, resp)
+		return
+	}
+
+	updatedMessage, err := model.UpdateMessageBody(m.DB, msg, requestMessage.Body)
+	if err != nil {
+		resp := httputil.NewErrorResponse(err)
+		c.JSON(http.StatusInternalServerError, resp)
+		return
+	}
+
+	c.JSON(http.StatusOK, gin.H{
+		"result": updatedMessage,
+		"error":  nil,
+	})
 }
 
 // DeleteByID は...
diff --git a/himu/model/message.go b/himu/model/message.go
index 3c73f19..54194d0 100644
--- a/himu/model/message.go
+++ b/himu/model/message.go
@@ -71,7 +71,16 @@ func (m *Message) Insert(db *sql.DB) (*Message, error) {
 }
 
 // Mission 1-1. メッセージを編集しよう
-// ...
+func UpdateMessageBody(db *sql.DB, msg *Message, newBody string) (*Message, error) {
+	if _, err := db.Exec(`update message set body = ? where id = ?`, newBody, msg.ID); err != nil {
+		return nil, err
+	}
+	return &Message{
+		ID:       msg.ID,
+		Body:     newBody,
+		Username: msg.Username,
+	}, nil
+}
 
 // Mission 1-2. メッセージを削除しよう
 // ...
diff --git a/himu/server_test.go b/himu/server_test.go
index 8e495e3..9f12994 100644
--- a/himu/server_test.go
+++ b/himu/server_test.go
@@ -181,6 +181,27 @@ func TestHelloWorldBotが反応する(t *testing.T) {
 	}
 }
 
-func TestAPIが指定したIDのメッセージを更新する(t *testing.T) {}
+func TestAPIが指定したIDのメッセージを更新する(t *testing.T) {
+	req, err := http.NewRequest(http.MethodPut, tsURL+"/api/messages/1", bytes.NewBuffer([]byte(`{"body":"testmessage"}`)))
+	if err != nil {
+		panic(err)
+	}
+	res, err := http.DefaultClient.Do(req)
+	if err != nil {
+		t.Fatalf("failed to send request: %s", err)
+	}
+	defer res.Body.Close()
+
+	b, err := ioutil.ReadAll(res.Body)
+	if err != nil {
+		t.Fatalf("failed to read http response, %s", err)
+	}
+
+	expected := `{"error":null,"result":{"id":1,"body":"testmessage","username":"sampleuser"}}`
+	actual := strings.TrimRight(string(b), "\n")
+	if actual != expected {
+		t.Fatalf("response body expected %s, but %s", expected, string(b))
+	}
+}
 
 func TestAPIが指定したIDのメッセージを削除する(t *testing.T) {}