1. An ultrasound diagnostic device comprising: a contour extraction circuit configured to extract a first contour image from at least one of a plurality of ultrasound images obtained from spatially-successive examination positions and each including an image of a blood vessel, a contour image extracted from an ultrasound image being an image indicating a contour of the blood vessel and being extracted from an image of the blood vessel appearing in the ultrasound image; a specification circuit configured to receive, from a user of the ultrasound diagnostic device, specification information specifying a manual correction target ultrasound image among the ultrasound images and correction information indicating details of a manual correction that the user performs with respect to a first contour image extracted from the manual correction target ultrasound image; and a contour correction circuit configured to correct the first contour image extracted from the manual correction target ultrasound image according to the correction information to obtain a corrected first contour image in the manual correction target ultrasound image, wherein: the contour extraction circuit is further configured to (i) set, as a target ultrasound image, one of the ultrasound images that is obtained from an examination position adjacent to an examination position from which the manual correction target ultrasound image is obtained, (ii) set, with respect to the target ultrasound image, an initial contour image having a shape of the corrected first contour image in the manual correction target ultrasound image, (iii) perform a search with respect to the target ultrasound image by using the initial contour image set with respect to the target ultrasound image, and (iv) extract, from the target ultrasound image, a second contour image which is a contour image that is obtained as a result of performing the search with respect to the target ultrasound image.