An ultrasound diagnostic apparatus which observes an inside of a body of a subject based on ultrasound waves reflected from the inside of the body and obtained using an ultrasound probe, includes: a B-mode image generation unit which generates a B-mode image, based on the reflected ultrasound waves； a blood flow image generation unit which generates, based on the reflected ultrasound waves, a blood flow image representing a region of the body in which blood flows； a lumen contour extraction unit which extracts a lumen contour of a blood vessel, based on the blood flow image； a provisional adventitia contour setting unit which sets a provisional adventitia contour containing the lumen contour； and an adventitia contour extraction unit which extracts an adventitia contour of the blood vessel, using the B-mode image, and using the provisional adventitia contour as a first initial contour.
