An ultrasound diagnosis apparatus (1) includes an ultrasound probe (10) having a plurality of elements arranged therein, the ultrasound probe transmitting ultrasound toward a subject, receiving an ultrasound signal reflected off the subject, and outputting a received signal a device that changes a preset assumed sound speed with respect to an actual sound speed of the ultrasound transmitted toward the subject and a frame position calculation device (20) that determines similarity of each portion between each frame by using speckles in RF data or amplitude images based on two or more of the different assumed sound speeds and calculates frame positions, thereby determining similarity in a stable, uniform, accurate manner without lowering a frame rate.
