PURPOSE: To obtain sharp sound quality with a few noise by detecting a system tone at a speech channel(Sch), and performing a squelch operation when the tone is not received for a constant time.

CONSTITUTION: First of all, channel designation is received by issuing a call in a Cch(control channel), and when it is a designation signal addressed to its own station, the Sch is set, then, a counter is cleared to 0. And since no system tone is overlapped at the time of issuing a simultaneous command, a tone is outputted from a speaker. When it is not the simultaneous command, the state of a PT is checked, and the qualification of a reception state is performed when it is set at an OFF state. When the PT is set at an ON state, a transmission processing is performed. When a timer overflows, the tone and a carrier are judged. Next, when no clear-down signal is received, the counter is counted up by one. When the counter counts exceeding N, squelch control is performed.