To provide a reconfigurable packet switch, with which an optimum circuit configuration can be automatically reconstructed in real time without requiring setting from the outside.

In this packet switch, the state of an inputted variable length packet is monitored by a packet length monitoring part 40, an optimum fixed packet length is automatically decided from the result by a fixed packet length instructing part 50, and the circuit of selector parts 10-1 to 10-N, fixed length packet switch parts 20-1 and 20-2 and output buffer parts 30-1 to 30-N is reconfigured.