1. An ultrasound diagnostic apparatus which performs transmission and reception of an ultrasonic beam from an ultrasound probe toward a blood vessel in a subject and produces an ultrasound image based on a sound ray signal obtained by processing a reception signal output from the ultrasound probe, the ultrasound diagnostic apparatus comprising: a candidate vascular wall boundary point determiner which determines candidate vascular wall boundary points based on the sound ray signal; a first evaluation value calculator which calculates a first evaluation value representing accuracy of each of the determined candidate vascular wall boundary points as a vascular wall boundary point; a second evaluation value calculator which, by means of a sound ray signal in a predetermined depth range including the determined candidate vascular wall boundary points and a sound ray signal adjacent to the sound ray signal, calculates a second evaluation value representing similarity between the sound ray signal and the adjacent sound ray signal; a third evaluation value calculator which calculates a third evaluation value for determining the vascular wall boundary point from among the candidate vascular wall boundary points based on the first evaluation value and the second evaluation value; and a boundary determiner which determines the vascular wall boundary point based on the third evaluation value and determines a vascular wall boundary based on the determined vascular wall boundary point.