PURPOSE: To improve resolution in a phase difference detection and to attain a low power consumption and high resolution of a circuit by constituting the circuit so that the phase to be detected is oscillated in the direction of time axis against a reference phase.

CONSTITUTION: A sampling signal P0 indicating the timing to define the count value based on a phase signal CMP is formed and outputted by a sampling phase adjustment circuit 3. This signal P0 is moved in the time axis direction by one cycle of a clock signal CK during by the time when the counting value of a counter 6 is changed by 1 with the change of phase of the signal CMP. The phase of the signal P0 and a reference phase signal PR are compared by a phase comparison circuit 4 to output a phase difference signal PD having the pulse width corresponding to the phase difference, and the signal CK is counted 6 only during the signal PD is active and the counted values are outputted to an average value arithmetic circuit 7. Then, the average value of counted values S within a specified period e.g., two cycles period of the reference phase signal is obtained by the circuit 7 and outputted as the measurement result M.