1. An ultrasound diagnostic apparatus which outputs an ultrasound diagnostic image of a subject to which an ultrasound contrast agent has been administered, the ultrasound diagnostic apparatus comprising: an imaging unit configured to form images each of which corresponds to one of echo signals received from the subject; a motion detection region setting unit configured to select a first image from among images which include images of the ultrasound contrast agent, select a second image from among images which do not include images of the ultrasound contrast agent, and set, as a motion detection region, a region in which an amount of image change between the first image and the second image is smaller than a predetermined amount, the images which include images of the ultrasound contrast agent and the images which do not include images of the ultrasound contrast agent being included in the images formed by the imaging unit; and an output unit configured to output, as the ultrasound diagnostic image, the second image on which a position adjustment has been performed to match a position of the motion detection region set by the motion detection region setting unit and a position of a region included in the second image and similar in an image feature to the motion detection region.