An ultrasound diagnostic apparatus includes a region of interest setter which sets a region of interest on a B-mode image, a controller which performs transmission and reception of ultrasonic beams with forming transmission focuses at a plurality of points set on sound rays at a shallower position and a deeper position than the region of interest to acquire reception data for sound speed measurement, and a sound speed calculator which calculates an average local sound speed value in the region of interest on the basis of reception data for sound speed measurement.