PURPOSE: To reduce the influence of noise and to extract a vertical synchronizing signal (VSS) by respectively changing the comparing reference value of a comparator in accordance with the detection of the start and end of the VSS in the case of extracting the VSS from a composite synchronizing signal.

CONSTITUTION: In the case of digitally obtaining a VSS from a composite synchronizing signal, the comparing reference value of the comparator 2 is respectively changed in accordance with the detection of the start and end of the VSS by using an up-down counter 1, the comparator 2 and a selector 3 for determining the comparing reference value of the comparator 2 to remove a noise component included in the composite synchronizing signal.