PURPOSE: To provide a B-mode image reduced in deterioration of luminance by measuring a distance from the ultrasonic echo sounding transducing surface of an imaging probe to a main body surface and automatically regulating luminance of a B-mode displayed based on the obtained distance information.

CONSTITUTION: A water tank 14 of a shock wave applicator 10 is placed on a main body surface P to measure a distance between an ultrasonic echo sounding transducing surface 24a of an imaging probe 20 and a main body surface P. A CPU 22 retrieves given gain pattern information from a gain data memory 46b of a memory circuit 46 based on the distance information. Consecutively, the CPU 22 executes B-mode photographing based on the retrieved gain pattern information through control of each part after it waits for selection of B-mode photographing of a console 90. The CPU 22 displays an excellent B-mode image, reduced in deterioration of luminance in the direction of a deep part, on a display part 80.