When someone gets involved in one certain task with others, he will adjust his actions according to not only internal feedback, but also observations of others’ behavior. In this paper, we propose a self-organizing agent that autonomously changes its behavior through observing the behavior of others by using SOM (Self-Organizing Map). This paper will give the results of multi-agent simulation on the cleanup problem concerning tasks of picking up garbage and throwing it away. Cooperative and altruistic behavior is evoked even though each agent has the simplest purpose of discarding more garbage by himself.