An ultrasound diagnostic apparatus includes a determining unit adapted to determine a depth position of a boundary of the intima-media complex at the clear boundary sound ray, and ascertain a depth position of the boundary of the intima-media complex at the unclear boundary sound ray; and an calculator adapted to calculate an intima-media complex thickness based on the depth positions of the boundary of the intima-media complex, wherein the determining unit performs pattern matching on a sound ray signal corresponding to the unclear boundary sound ray by using a sound ray signal corresponding to a clear boundary sound ray lying adjacent to the unclear boundary sound ray as a reference signal, thereby ascertaining the depth position of the boundary of the intima-media complex at the unclear boundary sound ray.