void MonsterDoAction()
    {
        GameActor target_game_actor = null;

        for (int i = 0; i < entities_.Count; ++i)
        {
            target_game_actor = ((GameActor)entities_[i]);
            if (!target_game_actor.isAlive())
            {
                continue;
            }
            if (target_game_actor.Type() != ActorType.monster)
            {
                continue;
            }
            if (target_game_actor.action_point > 0)
            {
                target_game_actor.DoAction();
            }
        }
    }