A scanning line immediately above a blood vessel is detected using a received signal of a reflected wave of an ultrasonic wave transmitted to the blood vessel, and candidates for front and rear walls of the blood vessel are detected based on the received signal of the scanning line. Then, vascular front and rear walls pairs of front and rear walls are narrowed down from the candidates, and the narrowed-down vascular front and rear walls pair is regarded as one blood vessel and artery/vein identification is performed for each blood vessel. Measurement of vascular function information is performed for the blood vessel determined to be an artery. Determination of an artery/vein is performed based on the relative relationship between the contraction time and the expansion time of the blood vessel.
