PURPOSE: To prevent radio interference and to make communication effective, by stopping automatically a transmitting radio wave if a slave equipment is in use even when the manual hook switch of another slave equipment is operated for radio communication between a master equipment and plural slave equipments.

CONSTITUTION: A telephone circuit is connected to the master equipment and plural equipments each provided with a receiving circuit 9 and a transmitting circuit 8 are provided in the state apart from the master equipment, performing the radio communication between the master equipment and plural equipments. The receiving circuit 9 of every slave equipment is provided with an IF signal detecting circuit 29 and a voice output controlling circuit 28 which amplifies a call signal selectively. Output signals of both circuits 28 and 29 are monitored by a circuit monitoring circuit 30. The switch circuit 35 consisting of transistors 31∼34 is controlled by the output signal of the circuit 30. Then, while some slave equipment is in communication with the master equipment, the circuit 35 is controlled by the output of the circuit 30 to stop a transmit radio wave from the transmitting circuit 8 automatically even if the manual switch 38 of another slave equipment is operated, preventing radio interference by the plural slave equipments.