To process data obtained by receiving ultrasonic waves by a simple method in ultrasonic diagnostic equipment.

Data after logarithmic transformation is stored in a low-order 8-bit portion 42 of an integer format 40, and the data Xi is shifted in an 8-bit portion 52 of a logarithmic part in a floating decimal format 50 as it is. Thus, as for the data after logarithmic transformation, a data expression format can be returned to that before logarithmic transformation without increasing a data amount. Under the data expression format, data processing of weighting addition can be performed by simple linear addition. In order to return the data format to that after logarithmic transformation again as for the data after data processing, reverse transformation from the floating dismal format 50 to the integer format 40 is performed.