This study investigated the pretend play by three-year olds, who newly entered a kindergarten, and their teacher. The investigators observed children's and their teacher's activities at free-playtime, once a week from April to July. The results of the observation show that in a sandbox, the children mainly enjoyed pretending to proper food with sand and water, occasionally changed their parts and plots about the play, and interacted with their teacher more frequently than their peers, while the teacher accepted and adapted children's intention in their play, tried to lead them to have a representative response jointly, and encouraged them to interact with mutually. Lastly, it was considered that the teacher played a role of a safety base for three-year-olds and contributed to new relationships between them.