An ultrasonic probe and a transmitter/receiver scan a 3D region using ultrasonic beams by raising the scanning line density of the transmission of ultrasonic beams for a region of interest compared to the scanning line density of the transmission of ultrasonic beams for regions other than the region of interest among the 3D regions. An image-generating part generates ultrasonic-image data of the 3D region, based on the received beams that have been obtained by the scan.
