Measurement data of a blood vessel is generated based on a measurement result of the blood vessel obtained by a blood vessel diameter measurement unit, and a breathing period estimating section estimates a breathing period corresponding to a breathing cycle based on the measurement data. A blood pressure calculating section calculates blood pressure relevant to the blood vessel based on the measurement data. An average calculating section calculates the average of the blood pressure calculated by the blood pressure calculating section in the breathing period estimated by the breathing period estimating section.
