PURPOSE: To ensure the detection of phase with high precision, by detecting the difference of phase between the 1st pulse input signal and the 2nd pulse input signal having a longer period than the 1st pulse input signal with a time width longer than the width of the 1st pulse input signal.

CONSTITUTION: A phase comparator works by an integration circuit consisting of a capacitor C1, a constant current source 22 and an SW1 and in the 1st section from the input of the pulse of the 2nd pulse input signal through the input of the pulse of the 1st pulse input signal. A level holding circuit consisting of a capacitor C2 and an SW2 holds the result of integration for the 2nd section from the lapse of the 1st section through the input of the pulse of the 1st pulse input signal. Then the integration circuit is initialized by a resetting circuit consisting of an SW3 for the 3rd section from the lapse of the 2nd section through the input of the pulse of the 2nd pulse input signal. Thus each operation is doen with high accuracy since each section has a width longer than that of the 1st input signal.