The present invention is configured to compare an output result of frequency analysis of a frequency gradient time-series waveform of a biosignal with preset corresponding data of output results of brain waves of different biological states to the output result. Accordingly, it is possible to estimate a time-series variation of a biological state which is specified by a brain wave state and brain waves by using a biological index other than brain waves, in particular, a result of frequency analysis of a frequency gradient time-series waveform of a biosignal reflecting an autonomic nervous function. Using an electroencephalograph is not required, and thus it is possible to estimate brain waves and a biological state corresponding to brain waves easily and rapidly.
