We have developed a new communication robot, Robopal, which is an indoor/outdoor robot for use in humanrobot interaction research in the context of daily life. Robopal's intended applications involve leading and/or following a human to a destination. Preliminary experiments have been conducted to study nonverbal cues associated with leading and following behavior, and it has been observed that some behaviors, such as glancing towards the leader or follower, appear to be roledependent. A system for representing these behaviors with a state transition model is described, based on four kinds of interaction roles: directive, responsive, collaborative, and independent. It is proposed that behavior modeling can be simplified by using this system to represent changes in the roles the robot and human play in an interaction, and by associating appropriate behaviors to each role.