Advances in information technology are changing the social environment, and have brought about the so-called information-oriented network society. One of the major issues in the network society is how to bring people together, that is how to form the communities that share similar interests. The formation of communities brings a great deal of benefits to the members such as social collaboration on the Internet, recommendations from people who are interested in similar topics, etc. However, acquiring information about communities and selecting appropriate communities to join is a burden for most of the people and the burden restricts their lives in the network society. In this paper, we propose a model of community formation with multi-agents with consideration of the cognitive balance model of the user. Personal agents can help the users by gathering and exchanging information, and recommending or assisting the users in making choices. The proposed model is evaluated through experiments.