PURPOSE: To measure the phase difference with high precision, by measuring and holding and calculating the time difference between the leading edge of a reference phase signal and the leading edge of the 2nd pulse of a signal to be measured, and a one-cycle time and a two-cycle time from the leading edge of the reference phase signal, by a spcified slanting waveform.

CONSTITUTION: When a request to measure the phase difference is inputted to a measurement controller 7, a rise detector 1a detects the leading edge of the reference phase signal to the time (a) from the time of the leading edge of the reference phase signal is detected until a rise detector 1b detects the leading edge of the 2nd pulse of the signal to be measured in omitting the 1st pulse. Further, the time (b) from the leading edge to the next leading edge of the reference phase signal, and the time (c) to the leading edge in omitting the succeeding one are found. The times (a), (b), and (c) are measured successively by a specified slanting waveform generator 4, and held in a digital computer 6 through an A/D converter 5. Therefore, the computer 6 calculates and outputs the phase difference without any influence of the error due to temperature drift and delay.