A wavelet conversion means (13) for subjecting brain wave data in a single trial to wavelet conversion, a wavelet coefficient window means (15) for extracting a predetermined area by a wavelet coefficient window from a wavelet coefficient surface obtained by the wavelet conversion, and a brain wave data discriminating means (17) for discriminating brain wave data by judging whether or not the predetermined area is extracted are provided to automate the work to extract distinguishing patterns from individual (in a single trial) brain wave data and to obtain averaging of the brain wave data. By considering whole of wavelet conversion coefficients, averaging and extraction of a vertex latency of distinguishing patterns can be executed without significantly losing the information of original waveform data.