PURPOSE: To make it possible to listen either one of sound of a master or a slave display and to listen simultaneously them by providing a sound switching means and the like that outputs selectively or simultaneously the first sound signal corresponded with the first video signal and the second sound signal corresponded with the second video signal.

CONSTITUTION: A control means 9 outputs the first control signal that makes the first video alteration switch 11 and the second video alteration switch 12 to switch with interlocking corresponding to a control indicating signal from an operating means 8 and the second and the third control signals that make the first and the second sound alteration switches 13 and 14 to switch respectively. The first and the second sound alteration switches 13 and 14 select and output either one of the first sound signal from a sound FM detecting circuit 7 or the second sound signal from a video tape recorder etc. with responding to the second and the third control signal respectively and give it to low frequency amplifiers 17 and 18.