PURPOSE: To attain efficient switching by applying switching the processing sequentially serially with plural channels set with 3rd/4th channel setting means, thereby attaining simultaneously processing with one set of the hardware constitution.

CONSTITUTION: When one route is faulty, an alarm is generated from an alarm generator, the alarm is detected by an AIS detection circuit 50a(1) and an alarm detection signal is sent to a relay switch circuit 13. Thus, the relay switch circuit 13 is switched to a and route, a multiplex signal is selected and sent to a terminal equipment. Thus, the relay switch circuit 13 uses one of 3-state buffer to process plural channels simultaneously, the required number of processed channels is set optionally and other channels are used for the other purpose.