We propose a framework for a robot to participate in and activate multiparty conversation. In multiparty conversation, the robot should select its behavior based on both linguistic information and participation structure. In this paper, we focus on multiparty conversation game "Nandoku," which is often played in elderly care facilities. The robot acts as one of the participants, and tries to promote the communication activeness. The framework handles the dialogue situation from three aspects: multiparty conversation, game progress and communication activation, and selects the most effective robot's behavior according to these three aspects.