PURPOSE: To control a channel unit of an opposite device optimizingly in the voice suppression and AIS state by providing a digital data controlling optimizingly the channel unit of the opposite device to a loaded channel unit, latching the data to a multiplex unit and sending the latched data to the opposite device when the unit is removed.

CONSTITUTION: A selector 14 of a multiplex unit 20 sends a data on a 1st line L1 from a voice channel unit 1a to a multiplexer circuit 15 when the voice channel unit 1a is loaded to the system. The multiplexer circuit 15 inserts a synchronization pattern into the data from the voice channel unit 1a and outputs the result to the opposite device from a PCM output terminal 16. When the channel unit is not loaded, a unit load information monitor circuit 18 stops the latch of a nonuse digital information latch circuit 17 and sends a selection signal to select nonuse digital information outputted and latched from a nonuse digital information latch circuit 17 to the selector 14.