A probe irradiates an ultrasound wave to an object to induce a shear wave and first elasticity information is obtained according to a first calculating scheme. An internal region of interest of the object is set based on shear modulus values included in the first elasticity information. Second elasticity information is obtained based on the shear wave induced to the internal region of interest, according to a second calculating scheme. Accurate elasticity information is acquired by using the first and second elasticity information to obtain third elasticity information from which an elastography image is generated for display to a user.