Since the number of people with dementia in Japan is growing, prevention of dementia or improvement of its symptoms are increasingly required. To address this problem, we constructed a system which reduces risk factors for dementia using a cooperative operation robot and an obstacle course activity for the elderly. This robot and the activity enabled players to communicate effectively and increase collective efficacy. We conducted experiments using the cooperative operation system with eight healthy elderly subjects. The subjects expressed more positive feelings, increased the time spent in conversation, and exercised more by swinging their arms during cooperative operation than during single operation. These results show that the cooperative operation robot and activity we developed helped elderly people to improve their collective efficacy. Therefore, this system may have a role in reduction of risk factors for dementia in the elderly.