This paper proposes a robot which activates group conversation of older adults by reusing the utterances of older adults who can activate group conversation. A novel social interaction support method named "coimagination" was used for collecting conversation data. Participants of coimagination sessions bring their stories with images according to the topics and share them with imagination through group conversation. The collected utterances were implemented on the robot. The robot got more laughter successfully than that of other human participants.