PURPOSE: To automatically identify a video signal of an input line of a video processing circuit switching a reception video signal of a television tuner or an external video signal through withdrawal of a plug and plug-in from/to an input jack of 1 circuit 1 contact.

CONSTITUTION: The device is provided with a buffer amplifier 16 outputting a DC of a prescribed level to a equipment video signal of a television tuner 2 as a bias signal, an input jack 5 of 1 circuit 1 contact of 3-line interrupt jack configuration connecting an output line 4 of the buffer amplifier 16 to an input line 10 of a video processing circuit 9 when no plug is plugged thereto and opening both the lines 4, 10 to apply an external video signal of the plug to the input line 10 when the plug is plugged thereinto, an integration circuit 17 integrating a signal of the input line 10 to detect its DC level, and a level identification circuit 18 comparing the detection level of the integration circuit 17 with a threshold level thereby identifying the supply state of the equipment video signal and the supply state of the external video signal.