A pressurizing/depressurizing section (4) performs at least one of air feeding to a cuff (20) by way of an air way (3) and air discharging by way of the air way (3) to thereby increase or decrease an internal pressure of the cuff (20). A first controlling section (5) causes the pressurizing/depressurizing section (4) to initiate the air feeding while performing the air discharging to thereby cause the internal pressure to transit from a pressure transient state to a pressure steady state or from the pressure steady state to the pressure transient state. A determining section (6) determines Whether the internal pressure has transited to the pressure steady state by way of the pressure transient state. A second controlling section (7) causes the pressurizing/depressurizing section (4) to suppress or stop the air discharging while continuing the air feeding, in accordance with determination made by the determining section (6).
