An ultrasound diagnostic apparatus includes a region-of-interest setting unit for setting a region of interest in the B mode image, an abdominal wall detector for detecting an abdominal wall of the subject in the B mode image, a controller for controlling a transmission circuit and a reception circuit to transmit a ultrasonic beam emitted from the transducer array and so steered as to enter the abdominal wall detected by the abdominal wall detector vertically with forming transmission focuses respectively at a plurality of points set in and near the region of interest to obtain reception data for measuring a sound speed, and a sound speed calculator for calculating local sound speeds in the region of interest based on the obtained reception data for measuring a sound speed.
