An electronic monometer (1) detects pressure within a cuff (2) at which an amplitude of change in a volume of an artery of a measurement subject becomes a maximum by detecting volume of an artery of a measurement subject while superimposing a vibration of high frequency during a period of raising the pressure to apply on the cuff (2) or during a period of lowering after raising to greater than orequal to a systolic blood pressure of the measurement subject. The electronic manometer (1) controls the pressure to apply on the cuff so that the volume of the artery of the measurement subject becomes constant, and measures the blood pressure of the measurement subject from an increased or decreased value of the pressure to apply.