diff --git a/app/controllers/tasks_controller.rb b/app/controllers/tasks_controller.rb
index 54050fb6..3a19096e 100644
--- a/app/controllers/tasks_controller.rb
+++ b/app/controllers/tasks_controller.rb
@@ -66,7 +66,8 @@ def update
   end
 
   # DELETE /tasks/1 or /tasks/1.json
-  def destroy
+  def destroy 
+    ActionItem.find_by(task_url: "/tasks/#{@task.id}").update(task_url: nil)
     @task.destroy
     respond_to do |format|
       format.html { redirect_to tasks_url, notice: "タスクを削除しました" }