To locally adjust luminance separately from the whole image and to realize an overall observation and a local observation by adjusting the luminance in a concerned region when the concerned region is set at the desired position on the ultrasonic image.

A region of interest(ROI) setter 17 is a means used by a user to set an ROI, and it is formed with a rack ball or a mouse. The coordinate information 102 indicating the outer frame of the set ROI is outputted to a region discriminator 24. The region discriminator 24 judges the luminance information with the coordinate information 102 of the ROI used as a reference, outputs the adjustment curve set by a first luminance adjustment curve setter 32 to a luminance regulator 26 as adjustment information when the luminance information is from within the ROI, and outputs the adjustment curve set to a second luminance adjustment curve setter 34 when the luminance information is from outside the ROI. The luminance regulator 26 makes a luminance adjustment, i.e., a gain adjustment, and a contrast adjustment according to the luminance adjustment curve set by the region discriminator 24.