A method of calculating a displacement of a shear wave includes inducing a shear wave in a body, obtaining a plurality of propagation frames including propagation information of the shear wave from an echo signal received from the body, determining a reference frame from among the plurality of propagation frames, and calculating a displacement of the shear wave based on the plurality of propagation frames and the reference frame. A shear modulus may be calculated by using a displacement of the shear wave after the displacement of the shear wave is calculated by comparing the reference frame and propagation frames. A mechanical modulus may be obtained by selecting an ultrasound image as a reference image after a shear modulus is calculated.
