In the ultrasound diagnostic apparatus, the ultrasonic wave transmitter/receiver transmits an ultrasonic beam to a subject, receives an ultrasonic echo that is a reflected ultrasonic beam from the subject, and outputs reception data and the ambient sound speed calculator acquires first reception data for calculating an ambient sound speed as a sound speed in the subject, which is data of a lower frequency than second reception data for producing a brightness image of the subject, and analyses the acquired first reception data to calculate the ambient sound speed.
