Is it possible to offset plural obligations among more than three persons? Although Japanese Civil Code only provides the "bilateral set-off" and the "triangle set-off", Japanese authors think that the "multilateral set-off" is possible by arrangements. But still, the structure of multilateral set-off has not been clear. Because of that, the Legislative Council of the Ministry of Justice discusses to introduce a new institution named the "triangle novation" at the Japanese Civil Code Reform. In this paper, we will argue that the multilateral set-off can be rationally explained without introducing such a new institution. With this view, we will briefly make sure that the Japanese Civil Code regulates the triangle set-off by special provisions and that the set-off can be occurred among three persons. Then, we will examine the "triangle novation" and its problems. Finally, we will discuss the structure of multilateral set-off by referring a recent French theory. In Japan, the meaning of set-off is broad. It includes not only the bilateral set-off but also the multilateral set-off. Whatever form it takes, the set-off is based on a function of balancing credits and debts. That function provides a simple settlement method among three or more persons in the same way as between two persons.