To provide a subject having no oppressive nor uncomfortable feeling with tightening by detecting a pulse wave generated by circulation of the blood of the human body, differentiating it twice so as to calculate the acceleration pulse wave, and calculating the highest blood pressure value, the mean blood pressure value, and the lowest blood pressure value based on the waveform.

A pulse wave detection means 1 is fixed to the finger tip 5 by a fixing tool, a light including, for example, 5000-8000 wavelength light is emitted from a luminous element 1-a, the transmission light transmitted through the finger tip 5 is received by a light receiving element 1-b, and it is converted into an electric signal matched with the light quantity received through a converter circuit 1-c so that the increase/decrease in the blood quantity by the pulsation of the heart is taken out as the electric signal. The signal expressing the increase/decrease in the blood quantity is outputted from a pulse wave detecting means 1 to an acceleration pule wave output means 2, the signal is made to pass through a two-stage differentiating circuit by the acceleration pulse wave output means 2 so as to be differentiated twice, and the acceleration (accelerating pulse wave) of the pulse wave is calculated so as to be outputted to a blood pressure value computing means 3.