In the ultrasound diagnosis, a probe performs transmission of an ultrasonic beam a plurality of times so as to form predetermined transmission focus points, the analog reception data output by the probe is A/D converted to turn into a first element data, a plurality of first element data is used to generate a second element data corresponding to any one of the plurality of first element data, and a sound velocity is determined using the first element data in a case where the position for determining the sound velocity is in a vicinity of the transmission focus point and using the second element data in a case where the position is not in a vicinity of the transmission focus point. In this manner, the sound velocity of the ultrasound waves in an inspection object can be accurately determined without decreasing the frame rate.
