PURPOSE: To use a buffer in common and to reduce circuitry by allowing a contention control means to send/receive plural input modules and control infor mation, and thereby avoiding cell contention when the cell is sent from the input module to an output port.

CONSTITUTION: A cell inputted from an input port 10 is multiplexed and written in a common memory 22 and a destination output port number and a write address are simultaneously stored in a memory 23. A selection circuit 24 selects a number of a head cell of the memory 23 and an address and outputs them to a common control section via a control section 25 and the common control section replies a link number of an output buffer section. The control section 25 discriminates the transmission to transmit enough to judge a cell when the reply signal indicates the signal is less than a link number of the output buffer section and reads the cell from the memory 22 and sends it to a spatial switch via a link 14. Thus, the contention of sending a cell simultaneously to the same output port is avoided and the circuit scale by means of the common use buffer is decreased.