A method employed in a prior art arm-worn blood pressure monitor to measure the height position of the heart has been an indirect method that merely estimates the position of the heart, and therefore has had the problems that the measurement accuracy and the reliability of the measurement are low, and that the measuring position is awkward and it is difficult to achieve correct position alignment. An arm-worn blood pressure monitor includes a cuff, a microwave transmitting unit for radiating a microwave onto a human subject, a microwave receiving unit for receiving a reflected wave Doppler-shifted relative to the radiated microwave due to a heartbeat of the subject, and a correct position detector for detecting, based on the reflected wave, whether the cuff worn around an arm of the subject is located in a correct position relative to the position of the heart of the subject.
