This paper reports our novel approach to developing a social robot. Such a robot reads human relationships from their physical behavior. We have developed an interactive humanoid robot that attracts humans to interact with it and, as a result, induces their group behaviors in front of it. In our approach, the robot recognizes friendly relationships among humans by simultaneously identifying each person in the interacting group. We conducted a two-week experiment in an elementary school, in which Robovie demonstrated proven reasonable performance in identifying friendships among the children. We believe this ability to read human relationships is essential to behaving socially.