Even when the reception scanning line is arranged outside the irradiation region of the focused transmission beam, reception beam forming is performed in which discontinuity does not occur near the transmission focal depth. The discontinuity extraction unit 113 detects the degree of discontinuity at which the wavefronts of the received signals or phasing signals received by the plurality of ultrasonic elements 105 are discontinuous. When there is an area where the degree of discontinuity is larger than a predetermined value, the discontinuity elimination delay time generation unit 114 changes the delay time of the area where the discontinuity occurs.集束型送信ビームの照射領域の外側に受信走査線を配置した場合でも、送信焦点深さ付近で不連続が発生しない受信ビームフォーミングを行う。 複数の超音波素子１０５が受信した受信信号または整相信号の波面が不連続となる不連続度合いを不連続抽出部１１３が検出する。不連続度合いが予め定めた値より大きい領域がある場合、不連続解消用遅延時間生成部１１４が、不連続を生じた領域の遅延時間を変化させる。
