The purpose of the present invention is to perform imaging with high real-time performance, and high frame-rate encoding transmission/reception. A plurality of transmitting aperture groups each including two or more transmitting apertures are sequentially caused to simultaneously transmit space-coded ultrasonic waves to an imaging object. In this process, at least two consecutive transmitting aperture groups transmit ultrasonic waves so that regions irradiated therewith partially overlap. A receiving aperture receives echoes of the ultrasonic waves from the imaging object. An imaging point is set in the overlapping area of the regions irradiated with the consecutively transmitted ultrasonic waves. A received signal relating to the same imaging point is obtained for each of the two ultrasonic waves consecutively transmitted. The two obtained received signals are decoded to obtain decoded received signals relating to the imaging point.
