To prevent mis-display of a character in the case of on-screen display of a linked character with a switching video image by selecting any of plural cameras.

A switching output of a 1st changeover section 4 based on a command signal S1 is fed to a synchronizing separator section 5 and a 2nd changeover section 8. The 2nd changeover section is usually set to the position of a video signal. In the case of camera changeover, a control section 13 starts a timer section 6 and reads display character designation data D1 from a memory section 10 and sends the data to a character superimposing section 12. When a detection section 6 detects a synchronizing signal, a character superimposing section reads required character from a character ROM 11 to conduct normally the superimposing processing onto a video signal. On the other hand, when the synchronizing signal cannot be detected even the lapse of a prescribed time, a 2nd changeover circuit is switched to the position of a synchronizing signal generating section 7 and sends the synchronizing signal to the character superimposing section and sends the display character designation data again to the character superimposing section. Thus, the normal character superimposing processing is implemented.