PURPOSE: To use a comparator operationable at nearly a speed of an input signal by using a synchronizing signal period as a charging mode of a comparator and using other period as a comparison mode so as to eliminate the need for the mode changeover.

CONSTITUTION: A synchronizing recovery circuit 10 generates a rectangular wave signal synchronously with an inputted video signal. A signal of nearly 14.3MHz is supplied to each of latches 51∼5n as a clock pulse and a synchronizing signal is fed to each of comparators 41∼4n as a clock. Thus, the mode is continuously the charging mode during the synchronizing period and a prescribed electric charge is held in a summing capacitor 45. In periods other than the synchronizing period, the mode is always the comparison mode and a voltage charged in the summing capacitor 45 at the charging mode and the input VX are added and the result is compared with a voltage VT of an inverter 43. The voltage depending on the polarity is outputted from the inverter 43 and sampled at a high speed by the latches 51∼5n.