In super aged society, system that assists social activities of older adults is needed for cognitive enhancement. Group conversation is one of the social activities. One of the largest problems for older adults is the imbalance of participation to conversation. Our approach is to develop a system that assists group conversation of older adults, by evaluating speech duration and facial expression of each participant during conversation. It enables all participants evenly to take part in the conversation, which tends to be difficult for older adults. We analyzed 15 group conversations for calculating the parameters used for evaluating the conversation. The effectiveness of the system using the obtained parameters was validated through the experiment. The system which evaluates only speech duration of each participant and the system which evaluates both speech duration and facial expression of each participant during group conversation were compared by analyzing 8 group conversations for each. The results demonstrated that the system which evaluates both speech duration and facial expression of each participant can make all participants to take part in the conversation evenly and actively. We successfully developed the system that can support group conversation regardless of the contents.