PURPOSE: To improve remarkably the operability by detecting a synchronizing signal among signals inputted from each input terminal, detecting to which terminal a displayed signal is inputted by the synchronizing signal, using a logical circuit, switching selectively a television receiver to the said input terminal and displaying it on a screen.

CONSTITUTION: When no signal is given to both input terminals 8, 9, the level of an input of an OR circuit 20 goes to a low level, a switch 5 is controlled and a general television picture inputted from the antenna 1 is displayed on a display tube 7. In applying power of an adaptor (not shown) connected to the input terminal 8, the inputted video signal is subjected to separation and extraction of a synchronizing signal only by a clamp circuit 16 and a synchronizing extraction circuit 17, the result is converted into a continuous level signal (state display signal) at a level signal converting circuit 18, and the video signal inputted to the input terminal 8 is displayed on the display tube 7 via the switches 10, 5.