PURPOSE: To execute the control, while leaving an advantage for using a common area of a buffer common type ATM switch by controlling a cell whose arrival frequency is high in cells to be outputted to an output circuit in which congestion is generated.

CONSTITUTION: When congestion is generated in a buffer common type asynchronous transfer mode(ATM) switch 70, the generation of the congestion is detected by using an in-buffer cell number counter % and a switch congestion state deciding circuit 90. A control part 103 of a line interface circuit 1-n sets a cell whose arrival frequency is high in cells outputted to an output circuit which becomes the cause of generation of the congestion to an object of the control by using information related to the congestion of the inside of a switch transferred from a switch congestion state deciding circuit 90, and route information contained in a header of the switch, and a result of observation of an arrival frequency observing part 102. In such a way, while holding an advantage of the buffer common type ATM switch, the cell can be controlled, and a buffer memory 702 can be used with high efficiency.