A transmitting beamformer performs convergence transmission that forms a transmission focus of an ultrasonic beam in a subject. A receiving beamformer comprises a virtual sound source method-based delay amount calculation part that obtains delay amount of a received signal with regarding the transmission focus as a virtual sound source, and a correction operation part that corrects the delay amount obtained by the virtual sound source method-based delay amount calculation part depending on position of imaging point. Delay amounts can be thereby obtained with good accuracy for imaging points in a wide area.
