An ultrasound diagnostic apparatus (150) which observes an inside of a body of a subject based on reflected ultrasound waves (201) reflected from the inside of the body and obtained using an ultrasound probe (101), includes: a B-mode image generation unit (104) which generates a B-mode image (202), based on the reflected ultrasound waves (201)； a blood flow image generation unit (105) which generates, based on the reflected ultrasound waves (201), a blood flow image (203) representing a region of the body in which blood flows； a lumen contour extraction unit (106) which extracts a lumen contour (402) of a blood vessel, based on the blood flow image (203)； a provisional adventitia contour setting unit (107) which sets a provisional adventitia contour (407) containing the lumen contour (402)； and an adventitia contour extraction unit (108) which extracts an adventitia contour (401) of the blood vessel, using the B-mode image (202), and using the provisional adventitia contour (407) as an initial contour.
