A compressed state evaluation unit 19 acquires values of distortion changes Δε1 and Δε2 corresponding to reference regions R1 and R2 set in two different tissues from an elasticity calculation unit 13 to obtain the ratio Δε2/Δε1 thereof, and evaluates a compressed state based on the obtained the ratio. The evaluated compressed state in a target region is displayed in correlation with the target region to be displayed on a display unit 10. The compressed state is further evaluated based on a small change in the compressed state upon measurement of the elasticity data so as to guarantee objectivity and reproducibility of diagnosis with respect to benign/malignancy of the tissue lesion.