PURPOSE:To make accurate judgement on blood pressure by detecting change in magnitude between the amplitude and the threshold value of pulse wave, judging whether or not the first pulse signal after change is noise, and thereby judging each pulse wave signal corresponding to the maximum or the minimum blood pressure. CONSTITUTION:When the maximum blood pressure SYS is determined, the pulse wave signal 2 exceeding the threshold value TH1 is detected first, if the amplitude PA3 of the following pulse wave signal 3 exceeds the threshold value (PA2-C4), cuff pressure PS corresponding to the pulse wave 2 is judged as a maximum in blood pressure SYS. If the previous amplitude does not exceed the threshold value, but the amplitude PA4 of the following pulse wave signal 4 exceeds the threshold value TH1, and furthermore, if the difference in amplitude between the pulse wave signal 3 and the pulse wave signal 4 is equal to or more than a fifth specified value C5, the pulse wave signal 3 is judged that it is noise. On the other hand, when the amplitude PA3 does not exceed (PA2-C4), and when the amplitude PA4 of the following pulse wave signal 4 does not exceed the threshold value TH1 or when the difference in amplitude between the pulse wave signal 3 and the pulse wave signal 4 is less than the fifth specified value C5, the pulse wave signal 2 is judged that it is noise. By this constitution, the position of the maximum blood pressure can be accurately specified, so that reliability can remarkably enhanced.
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