1. An ultrasonic diagnostic apparatus comprising: a data acquisition unit configured to acquire a plurality of ultrasonic data by repeatedly scanning a two-dimensional section including a target blood vessel with an ultrasonic wave; an image generation unit configured to generate a plurality of ultrasonic images by using the plurality of ultrasonic data; a calculation unit configured to calculate a feature amount for determining a shift between the two-dimensional section and a central axis of the target blood vessel in a running direction on the each ultrasonic image; a determination unit configured to determine an optimal image from the plurality of ultrasonic images based on the feature amount; and a measurement unit configured to measure an intima-media thickness of the target blood vessel by using the optimal image.