A method of generating a diagnostic image of a subject including transmitting a transmission signal to the subject acquiring a first RF frame and a second RF frame from an echo signal reflected from the subject estimating a second directional displacement indicating a degree of movement of a first point of the subject appearing in the first RF frame in the second RF frame generating an ultrasonic image corresponding to the second RF frame and correcting an error of the generated ultrasonic image using the estimated second directional displacement. The first point may appear in the first RF frame and the second RF frame.
