In order to three-dimensionally quantify the elastic information indicating the hardness or softness of tissue of an object with a simple operation, two three-dimensional regions of interest are set on a displayed elastic rendering image. A three-dimensional distortion ratio measuring unit 52 calculates a ratio between elastic information in the set first three-dimensional region of interest and elastic information in the set second three-dimensional region of interest and displays the ratio on an image display device 13.
