A transmitting/receiving circuit drives an ultrasonic probe in accordance with a trigger signal based on an electrocardiographic waveform under the control of a control device so as to scan a plurality of regions, and obtains scan data for each region. During the scanning, the circuit causes the probe to scan the respective regions so that scan data in which time phases of the electrocardiographic waveform substantially coincide are obtained in the vicinities of the boundary between at least two adjacent regions among the regions. That is, in adjacent regions, the circuit causes the probe to scan the respective regions in the main or sub-scanning directions set to be reverse to each other. Further, an image processor generates ultrasonic image data of the range in which the regions are joined, on the basis of the scan data obtained by starting scanning at the same time phase.