A pressing cuff(13) presses a pressure sensor (11) above an artery. The level of the pressure applied to the pressure sensor (11) is changed while the pulse wave is measured based on information about the pressure from the pressure sensor (11). In order to adjust the level of the applied pressure using the pressure of gas in the pressing cuff (13), a three-port valve (16) and a two-port valve (15) are controlled so that the connection is changed to establish a state of holding the amount of the gas in the pressing cuff (13). Then, the state is changed to a state of isolating and discharging gas in which a part of the held gas is isolated from the remaining amount of the gas to be discharged. Then, the state is changed to the state of holding the remaining amount of gas in the pressing cuff (13).
