A transmission and reception unit repeatedly scans a three-dimensional scanning area including a specific part of a patient with an ultrasonic beam via an ultrasonic probe. A volume data set generation unit generates a plurality of volume data sets whose scanning times different from one another in accordance with the output from the transmission and reception unit. A section image generation unit respectively generates the data of a plurality of the section images concerning the predetermined section of the specific part based on the plurality of the volume data sets. An image display unit displays the plurality of section images by changing at least one of the position and the size of each of the plurality of section images against the display area in accordance with variation of at least one of the position and the shape of the specific part on the plurality of section images.
