diff --git a/.github/workflows/development.yml b/.github/workflows/development.yml
index e87cac7..73646aa 100644
--- a/.github/workflows/development.yml
+++ b/.github/workflows/development.yml
@@ -25,10 +25,3 @@ jobs:
           apiToken: "${{ secrets.API_KEY }}"
           roomId: "${{ secrets.ROOM_ID }}"
           message: "${{ env.MESSAGE }}"
-      - uses: ./
-        with:
-          apiToken: "${{ secrets.API_KEY }}"
-          roomId: "${{ secrets.ROOM_ID }}"
-          message: "this is your task"
-          messageType: "task"
-          userIdsToAssignTask: "${{ secrets.USER_ID_1 }}"
diff --git a/README.md b/README.md
index fdf2c81..dda4004 100644
--- a/README.md
+++ b/README.md
@@ -22,6 +22,9 @@ Chatwork の Room にメッセージを送信する Action です。
     message: 'ここにメッセージを書きます。'
 ```
 
+> [!WARNING]
+> v1.1で導入されたタスク機能は、将来のバージョンから削除されます。代わりに[okuzawats/chatwork-task-action](https://github.com/okuzawats/chatwork-task-action)を使用してください。
+
 タスク機能にも対応しました（v1.1〜）。`messageType` と `userIdsToAssignTask` を追加してください。`userIdsToAssignTask` には複数IDを指定できます。カンマ区切りでユーザーIDを指定してください。
 
 ```yml
diff --git a/action.yml b/action.yml
index 4ab7c48..b77f2fb 100644
--- a/action.yml
+++ b/action.yml
@@ -12,6 +12,7 @@ inputs:
   roomId:
     required: true
     description: "Chatroom ID"
+  # deprecated inputs. this inputs parameter will be removed in the future version.
   messageType:
     description: "Message type to send. default is message."
     type: "choice"
@@ -23,6 +24,7 @@ inputs:
   message:
     required: true
     description: "Message to send"
+  # deprecated inputs. this inputs parameter will be removed in the future version.
   userIdsToAssignTask:
     required: false
     description: "User Id to be assigned to the task. Or you can specify multiple users, separated by commas. example 1,3,5"
@@ -36,6 +38,11 @@ runs:
         fetch-depth: 0
     - name: "set up ruby"
       uses: "ruby/setup-ruby@v1"
+    - name: "deprecate messageType"
+      if: ${{ !github.event.inputs.messageType }}
+      run: |
+        echo "::warning::messageType is now deprecated. If you use only message, just remove the parameter. Or if you use task, please use okuzawats/chatwork-task-action instead. In this case, remove userIdsToAssignTask parameter also."
+      shell: "sh"
     - name: "run action"
       run: |
         ruby $GITHUB_ACTION_PATH/main.rb