To accurately detect an amplitude of an input sine wave shaped signal by a simple composition.

An analog signal including a sine wave signal Ax.sin(2πFt+ψ) of a frequency the same as a known reference analog sine wave signal A0.sin2πft is input in an input terminal IN. An analog-to-digital converter 130 samples the input analog signal at a predetermined rate and subjects it to an analog-to- digital conversion. A sine wave coefficient calculating part 140a and a cosine wave coefficient calculating part 140b respectively calculate coefficients Csin1 and Ccos1 of each basis function by applying methods of least squares respectively using a sine wave function sin2πft and a cosine wave function cos2πft as basis functions. An amplitude calculating part 150a calculates the amplitude Ax of the sine wave signal Ax.sin(2πft+ψ) by executing computing of (Csin12+ Ccos12)1/2. A phase calculating part 150b calculates a deviated amount ψ of a phase of the sine wave signal Ax.sin(2πft+ψ) by executing computing of tan-1(Csin1/Ccos1).