PURPOSE: To branch a video signal to both a video signal processing unit and a video monitor without provision of a branching device by extending a video terminal without incurring deterioration in the quality of a video signal.

CONSTITUTION: The changeover device is provided with selector switches 26, 28 connecting to each of video terminals VT1, VT2 connecting to a video signal processing unit 21 and selecting either the video signal sent from controllers 22, 24 or the video signal sent from a terminal controller in a lower-stream video terminal to be relayed to an upperstream and with transmission reception circuits 31, 32 sending/receiving a signal for switching control of the selector switches 26, 28 with the video signal processing unit 21. Video amplifiers 27, 29 connected to an output terminal of the controller are provided and the video signal is relayed to an upper-stream via the video amplifiers 27, 29 and the selector switches 26, 28 and video monitors 23,25 in the video terminals VT1, VT2 are always connected to output terminals 22, 24 of the controller.