PURPOSE: To enable the setting of the optimum amplification factor automati cally in an ultrasonic diagnostic apparatus which performs a separate amplifica tion of an ultrasonic beam at each depth.

CONSTITUTION: One screen of echo data are stored into a frame memory 22. A plurality of reference areas are set for a scanning surface corresponding to each depth to generate histogram with a histogram conversion circuit 30 at each of the reference areas. A luminance value having a peak in the histogram is compared with a reference value α to judge an amplification factor from a difference value. The amplification factor is determined for each depth thereby executing STC.