A diagnosis apparatus and a method of operating the diagnosis apparatus. The diagnosis apparatus includes a probe for transmitting an ultrasonic wave signal to a subject and receiving a response signal a data generating unit for generating image data of a plurality of frames, based on the response signal a reliability determining unit for determining whether the image data is reliable by estimating a motion of the probe, based on the image data a diagnosis unit for generating diagnosis data about the subject by using elastography, based on the image data and a display device for displaying an image, based on the image data.
