//private void OnCollisionEnter(Collision collision)
    //{
    //       Debug.Log("AlertGameAreaLimit");
    //       StartCoroutine(AlertGameAreaLimit());
    //}

    public IEnumerator AlertGameAreaLimit()
    {
        UICtrl uiCtrl = FindObjectOfType <UICtrl>();

        uiCtrl.AlertTextSet("この先はゲームエリア外です");
        yield return(new WaitForSeconds(3.0f));

        uiCtrl.AlertTextOff();
    }