A transmission and reception unit controls probes to form an ultrasound beam which intersects a bone and obtains a reception signal. A beam evaluating unit evaluates an intersection state of the ultrasound beam with respect to the bone based on a shape of an envelope of the reception signal. More specifically, the beam evaluating unit determines a quality of the reception signal based on a height and a slope of a hill-like portion, included in the envelope, corresponding to the bone and evaluates the intersection state of the ultrasound beam.