To reduce current consumption and to improve noises by fixing the DC potential of a reference value at a potential corresponding to the central position of maximum amplitude of a video signal to be supplied.

This circuit is composed of a video signal input terminal 1, a clamp circuit 2 for fixing the synchronizing signal top end potential of the video signal constant, a reference DC voltage source 3 for determining the fixed potential of the clamp circuit 2, a differential amplifier 4, a signal output terminal 5 and a reference DC voltage source 6 for the differential amplifier 4. At this circuit, the DC potential of the reference value is fixed at the potential corresponding to the central position of maximum amplitude of the video signal to be supplied. Namely, the video signal inputted from the input terminal 1 is inputted to the differential amplifier 4 after the top end of the synchronizing signal is fixed at the constant potential determined corresponding to the reference potential of the reference DC voltage source 4 by the clamp circuit 2. At such a time, a reference voltage is applied to the other input of the differential amplifier 4 by the reference DC voltage source 6. Thus, the fluctuation of gain to the input level can be suppressed.