PURPOSE: To improve the convenience by designing the titled set that one of a handset or a base unit is hooked on so as to allow the other to be connected to an external line when a telephone call comes from the external line during intercom communication.

CONSTITUTION: A detection circuit 265 of the base unit 2 detects an incoming call during intercom talking and a ringer 266 and a speaker of a handset are energized. In this case, when the unit 2 hook on, the ringer 266 is hooked off and a control signal representing on-hook is transmitted from the unit 2, a bell tone of the set 1 is turned off, and a hybrid circuit 231 is connected to a telephone circuit 3 by a relay circuit 232. Thus, a telephone call from an external line is connected to the set 1 through the unit 2. Further, when a talk switch is changed over in the set to the incoming call during intercom talking, no transmission signal is transmitted, the ringer of the set 1 and the unit 2 is turned off, the transmission from the unit 2 to the set 1 is stopped, and a telephone set 4 is connected to the circuit 3 by a relay circuit 232. Thus, the external telephone call is connected to the telephone set 4.