Ultrasound measurement data is acquired from a blood vessel (3) through the surface of the body, the blood vessel having a branch point (4). The branch point is detected from A-mode data. Then, the distance that the ultrasonic probe (16) has moved on the surface of the body along the longitudinal direction of the blood vessel is determined from the B-mode image, and the user is notified when a predetermined position has been reached for performing a vascular function measurement (e.g. measurement of intima media thickness of a carotid artery). It is thus possible to realise accurate positioning of the probe at the same position on the blood vessel, e.g. for periodic measurements.
