PURPOSE: To effectively utilize a voice channel by providing a control part with the collecting line station of an exchange side and a subscriber station respectively and executing a local switching at the subscriber station without the use of a time slot for a voice between the subscriber station and the exchange.

CONSTITUTION: When a call is executed from a subscriber 11 to a subscriber 12, it is received by a subscriber circuit 7 for a to-subscriber, the calling signal is encoded at a signal processing part 15 and sent out to the collecting line station side by loading the time slot. When the calling signal is received at a collecting line station 2, a control part 9 reverse-converts the encoded calling signal and a subscriber circuit 5 for a to-exchange is turned to an ON condition. In the control part 9 of the collecting line station 2, a subscriber circuit 6 for a to-subscriber against an incoming signal 17 from the exchange to the subscriber 12 is turned to an ON condition and the loop of the exchange and the subscriber circuit is formed. Thus, even when all the voice channel is in use, the call can be executed to another subscriber in a same subscriber station and the voice channel is effectively utilized.