PURPOSE: To release a mode at which a reception signal is outputted to a speaker with a single telephone set without giving a load to a master device by releasing the mode at which the reception signal is outputted to the speaker when a prescribed signal is received.

CONSTITUTION: In the operation of on-hooking, a switch 106 is connected to a SW1A-side, and a channel between a main device interface part 105 and a handset 108 is secured. In the operation of off-hooking, the switch 106 is connected to a SW1B-side and the channel between the main device interface part 105 and a switch 107/non-connection is secured. If a system is in a speaker reception state when a cut request message is received from a main device 101, a control part 103 lights off speaker LED 113, turns off the speaker 111, transmits an on-hooking message to the main device 101 and the system transits to an idle state. When it is in a handset call state, the system is left as it is.