PURPOSE: To enable the radio call between the control station and each mobile station and between mobile stations, by using two channel frequencies with selection and changing over the tone squelch unit into operating and non-operating state.

CONSTITUTION: Normally, the control station 11 and the mobile station 13 make call in the communicating frequency 15 being the first channel CH frequency. In this case, the tone squelch unit of the second mobile station 14 is operative and the calls between the mobile stations 13, 14 and between the mobile station 14 and the control station 11 are disable respectively. Next, when the CH change-over switch is changed over to the correspondence frequency 16 of the second CH frequency at the mobile station 13, the tone squelch unit is released in synchronizing with this change-over, being transferred to non-operating state. Further, by the correspondence in the communicating frequency 16 with common wave with other zones splitting the communication enable range, the calls between the control station 11 and the mobile station 14, between the mobile stations 13 and 14, and between the control station 11 and the mobile station 13 can be made respectively.