When in order to receive the reflected wave of the acoustic secondary wave which is generated attendant upon the propagation of 1st vibrator 56A and the acoustic primary wave which transmit the acoustic primary wave which possesses two frequency components, seeing from the transmission direction of the acoustic primary wave, in order for the field where the reflected wave is received to be piled up with 1st vibrator 56A, the 2nd vibrator 56B which is laid out and, it possesses acoustic vibrator 56.音響振動子56は、二つの周波数成分を有する音響一次波を送信する第1の振動子56Aと、音響一次波の伝搬に伴って発生する音響二次波の反射波を受信するために、音響一次波の送信方向から見たときに反射波を受信する領域が第1の振動子56Aと重なるように配置された第2の振動子56Bと、を有する。
