In the diagnostic ultrasound apparatus, moving average processing is successively performed on a frame series with frame sets obtained from three kinds of frames, A, B, and C, as units, thereby successively generating compound frames. Each compound frame has a central sub-region and multiple peripheral sub-regions. In order to match the gain between the multiple sub-regions when generating each compound frame, a special compounding condition is applied to individual peripheral sub-regions. Specifically, processing that redundantly substitutes the same data value for multiple elements in the compounding computation equation is performed. Using such a spatial compounding, differences in gain between multiple sub-regions can be eliminated or reduced.
