PURPOSE: To improve the processing speed of phase detection by obtaining a phase angle from the average sampling value of input signals at two reference points of a reference signal.

CONSTITUTION: Sampling circuits 2 and 3 receive the input signal and the pulse signal of pulse generating circuit 4 respectively and sample the input signal at reference points θ0 and θ0+α of the reference signal. Next, integrating circuits 5 and 6 average respective sampling values to obtain average values of sampling values. Next, operating circuit 7 uses two sampling average values to perform the operation dependent upon the expression and obtains phase θ of the input signal for the reference signal. Thus, the processing speed of phase detection can be improved by simplification of sampling and omission of Fourier conversion.