To precisely calculate IMT by acquiring an ultrasonic image always at approximately the same area for the same subject, and to increase the accuracy of a diagnosis for arterial sclerosis and so forth.

A scanning image which is scanned at the present point for the subject is semi-transparently displayed in the screen of a monitor 22. At the same time, ultrasonic image data at the previous measurement time for the same subject is read from a past image storage unit 16, and is displayed in the same screen as a reference image. Also, a matching calculation unit 17 calculates an index value which evaluates the similarity between the scanning image and the reference image by the picture element unit, and the result is simultaneously displayed in the screen as a level indicator. An examiner adjusts the location or the direction of an ultrasonic probe 10 so that the scanning image may be approximately totally superposed with the reference image while watching a monitor 22 on which those displays are formed, and performs a freeze operation of the image by performing a fine adjustment so that the matching degree may become more optimal.