In recent years, avatars have been used for the communication in various situations including CG avatar used in the metaverse, robot avatar used in the real world and AR avatar used in the augmented reality world. In such avatar communication, several knowledge about the influence that the usage of avatar affects the user’s feeling and behavior has been obtained. In order to use the avatar effectively for the communication in the avatar society, it is necessary to construct a discipline that organizes these phenomena as avatar psychology. In this paper, the psychological research about the avatar such as Proteus effect, embodied knowledge, co-actor effect, and sense of collaboration that have been conducted in our laboratory are introduced.