PURPOSE: To make it possible to separate accurately a synchronizing signal from a composite video signal, etc., by using a fixed reference detection signal and LPF for noise removal.

CONSTITUTION: Composite video signal (a) is clamped by clamping circuit 7 to decrease its pedestal level down to zero V, and then suplied to FETQ2. Signal (a), on the other hand, is passed through conventional synchronous separator circuit 2, etc., to generate a sampling pulse of a sink-chip level, which is applied to the gate of FETQ2. Then, the potential of the sink chip of signal (a) is sampled, its output is supplied to LPF10 to remove a high-frequency component and the voltage of it is divided at a fixed ratio, so that a reference detection signal within ranges of the sink chip level and pedestal level of signal (a) will be obtained. Next, operational amplifier 12 compares signal (a) with the above-mentioned reference signal to separate a horizontal synchronizing signal. In this way, the stable reference signal and LPF for noise removal are used to make it possible to separate the synchronizing signal accurately.