An ultrasound diagnostic apparatus includes a region-of-interest setting unit for setting a region of interest in a given region of a B mode image, a controller for controlling a transmission circuit and a reception circuit to transmit ultrasonic beams composed of fundamental waves having a first frequency with forming transmission focuses at a plurality of points set in and near the region of interest and receive ultrasonic echoes having a second frequency, which is a harmonic component of the fundamental waves, thereby to obtain reception data for measuring a sound speed, and a sound speed calculator for calculating ambient sound speeds at the points based on the obtained reception data for measuring a sound speed.
