PURPOSE: To measure the fluctuation in blood pressure in training without restraining at every one heart beat.

CONSTITUTION: The light beams cast at prescribed cycles from light sources 1, 2 of different wavelengths are absorbed and reflected by the superficial blood vessels of a living body. The respective reflected beams are detected by a common photodetector 3 and the electric signal corresponding to the photodetected quantity is sent to a multiplexer 5. The multiplexer 5 separates the electric signal by each of the respective wavelengths and the separated electric signal are sent to variable gain amplifies 6, 7, by which the electric signals PR and PIR are obtd. These electric signals are inputted to band-pass filters 8, 9, from which pulse wave signals ΔPR, ΔPIR having the fluctuation component and disturbance component of the reflected beams by the blood vessel pulse wave are obted. These signals are inputted to a differential amplifier 10 to obtain a pulse wave signal PS from which the disturbance is removed. This signal is inputted to a differentiator 11, by which a differential pulse wave signal δPS is obtd. A differential electrocarbiograph waveform δCG is obtd. from an electrode 13 and an electrocardiograph 14. A pulse wave propagation velocity is obtd. from the both. The propagation velocity is sent from a transmitter 21 to a receiver. The blood pressure value of every one heart beat is estimated from this pulse wave propagation velocity.