Accuracy of spectrum analysis improves, and further reliability of information indicating tissue characterization of a living organ improves. A computation region, which is a target of frequency spectrum analysis, and a window region are set on a received signal. A plurality of received signals of the window region are weighted and the frequency spectrum analysis is performed on the received signals of the window region after the weighting. The weighting is performed by using weight distribution corresponding to strength distribution generated in the received signals of the window region in a case of assuming that the ultrasound transmitted from the plurality of transducers propagates as waves in the subject, reaches a target region in the subject which corresponds to the computation region, is reflected from the target region, then further propagates as waves in the subject, and reaches the plurality of transducers.
