PURPOSE: To switch sound signals smoothly by switching the output signals of 1st and 2nd sound reproducing devices provided corresponding to 1st and 2nd moving picture projectors by performing digital signal processing and the cross-fading processing of playback signals.

CONSTITUTION: When a 1st moving picture projector 1a projects an image on a screen, a 1st digital sound reproducing device 2a operates in synchronism with the time code of the 1st moving picture projector 1a. When the 1st projector 1a is switched to the 2nd projector 1b, those projectors are switched in the same way as usual, and a cross-fading processing circuit fades out the playback signal of the sound reproducing device 2a after a 2nd digital sound reproducing device 2b synchronizes with the time code of a film projected by the 2nd projector 1b, and then fades in the playback signal of the sound reproducing device 2b. Consequently, the sound signals are switched smoothly.