After 90's, the combination of Japanese Agricultural Co-operatives in large area has been rapidly promoted. In this study, the Combined Effects of Japanese Agricultural Cooperatives in large area were verified by comparing states before and after the combination. As a result, the Combined Effects were shown to the rise of the equity capital ratio and the increase of the holdings of mutual insurance in a long term per board member. Moreover, the other effects were shown to the standardizing the performances of Japanese Agricultural Co-operatives, the decreasing of the number of board members, and the rise of staff's salary level.