A measurement point is set at frame data consisting of an envelope signal obtained by orthogonal detection of an RF signal output from an ultrasonic probe before and after compression of an examinee. The measurement point is moved in the ultrasonic beam direction (first dimensional direction), second dimensional direction or third dimensional direction with respect to the frame data so as to obtain a position where the envelope signal correlation coefficient before and after compression belonging to a correlation window surrounding the measurement point becomes maximum. According to this, the displacement of the measurement point accompanying the compression is obtained and the phase difference between the RF signals before and after the compression is obtained, so as to accurately obtain a displacement of the measurement point accompanying the compression by displacement measurement means. Thus, it is possible to estimate the displacement distribution without being restricted by the displacement amount, reduce the calculation time, and cope with a horizontal direction displacement. <；IMAGE>；
