PURPOSE: To clearly recognize an incoming signal and to automatically control a sound volume by controlling the sound volume of a television receiver by detecting the transmission and reception signals of a telephone set, and superposing and displaying a mark representing the busy of the telephone set on the screen of the television receiver.

CONSTITUTION: A detection circuit 3 to detect the transmission and reception signals of the telephone set 2 is provided, and the AC component of input/output signal of the telephone set 2 is extracted, and is converted to a DC signal, and the presence/absence of the DC signal is used corresponding to the ON/OFF of a switching signal. The call signal of incoming can be converted to the DC signal even when the transmission/reception of the telephone set is set at an on-hook state. By the switching signal, a sound volume control circuit 4 to control the sound volume of the television receiver 1 in viewing at a low level, and a mark display circuit 5 to superpose and display the mark 6 representing the busy of the telephone set 2 on the picture of the television receiver 1 in viewing are started up. In such a way, it is possible to prevent speech disturbance due to voice energy outputted from the television receiver 1 from being generated, and to surely inform the incoming signal.