PURPOSE: To enable control over the level ratio of both video and audio carriers even when the amplitude ratio of the both is inverted, by detecting the ratio of both the carriers have been inverted and by controlling said level ratio using variation in the synchronization level of the video signal at the time of inversion.

CONSTITUTION: The output of low-pass filter 11, having a cutoff frequency of about 2 NHz, contains a synchronizing component and DC component, is synchronously separated by synchronous separator 12. The synchronously separated signal has the peak value detected by peak value detector 13, and when the DC voltage corresponding to the synchronizing peak value has ≥2 ratio, switching signal generating circuit 14 generates a switching signal. The switching signal is sent to switch 10 to change-over the voltage signal from differential amplifier 8 to the voltage of reference voltage 15, to control variable equalizer 3.