Reception beamforming that does not generate discontinuity in the vicinity of the depth of a transmit focus is executed even if reception scanning lines are disposed outside of the irradiation area of a focusing-type transmission beam. The degree of discontinuity showing the discontinuity of reception signals detected by plural ultrasound elements 105 or the degree of discontinuity regarding the discontinuity of the wave fronts of phased signals is detected by a discontinuity extracting unit 113. If there is an area where the degree of discontinuity is larger than a predefined value, a delay time generating unit 114 for discontinuity elimination changes the delay times in the area where the discontinuity is generated.
