PURPOSE: To measure correctly a phase difference of integer times as much as 360° or a phase difference of 1/N of 360°, without deteriorating the time resolution, by measuring the phase difference every period of a reference signal.

CONSTITUTION: A measuring signal A(t) is divided into two waves. One of these two waves is supplied to a quadrant deciding circuit 13 as a waveform (a), and the other is supplied to the circuit 13 via a delay circuit 11 in the form of a waveform (b). Then these two waveforms are displayed in binary numbers. A reference signal B(t) is shown by a waveform (d) and then turned into a waveform (e) to be used to a sample signal of the circuit 13. The gain/loss of phase is detected by counting the detecting signals given from a quadrant storing circuit 14 storing a 1-sample preceding quadrant and a direction deciding circuit 15 as up- or down-pulses of an up-down counter 16 respectively and then measuring a change of integer times as much as 360°.