To analyze waveforms highly accurately by obtaining a residual waveform and a minimal point cycle with the use of amplitudes of a sine waveform and a cosine waveform obtained by a product of waveform data and sine and cosine waveforms of a predetermined cycle, a product of the sine and cosine waveforms and squares of the sine and cosine waveforms, etc.

A sine wave component of a predetermined cycle included in a predetermined section of waveform data is obtained with the use of amplitudes of a sine waveform and a cosine waveform given by five values of a product of the waveform data and the sine and cosine waveforms of a predetermined cycle, a product of the sine and cosine waveforms, squares of the sine and cosine waveforms and an added value in the predetermined section. A predetermined minimal point cycle is obtained wherein the residual amount obtained by adding a square value of a residual waveform resulting from the subtraction of the sine waveform component from the waveform data in the predetermined section is minimum. An n-th sine wave component is sequentially obtained from an (N-1)th residual waveform with the use of one minimal point cycle. The sine wave component is repeatedly detected and removed in this manner.