PURPOSE: To perform stable measurement with high accuracy by constituting two circuits respectively measuring the mutual phase difference between two reference pulses having predetermined phase difference and the phase difference between a pulse to be measured and one reference pulse of delay elements.
CONSTITUTION: The first and second reference pulses P1, P2 and pulse P to be measured applied to input terminals 1 - 3 are applied to pulse phase measuring circuits 5, 6 to measure respective phase differences. These circuits 5, 6 are constituted of delay elements and the outputs thereof are integer outputs and the pulses P2, P are a barometer showing how many delay elements advance from the pulse P1. Therefore, accuracy corresponds to one delay element and high accuracy is possible. Since the phase difference between the pulses P1, P2 and that between the pulses P, P1 are measured by the same means, the temp. change and irregularity of the delay times of the delay elements can be almost neglected to make stable measurement possible.