To prevent the reduction of line use efficiency caused by the regulation of communication rate at all destination terminals in a line according to the worst value of destination terminals attached to a branching point.

A flow control loop at an ATM exchange 20-2, for example, corresponding to p-mp connection in an ATM network is divided for each branch, namely, for each branching point of connection and a switch at the branching point is provided with a buffer for temporarily storing data for each output port. Thus, even when there is a report instructing the congestion to several state report cells from plural downstream branches connecting a destination terminal 10-5 or the like, within the range in which the difference of upstream and downstream links in that case can be absorbed for the capacity of this empty buffer, the ATM exchange 20-2 reports information not instructing the congestion to the upstream link in the direction of transmission source terminal 10-1 with this state reporting cell.