PURPOSE: To obtain uniform diffraction efficiency in the entire operating frequency range by disposing plural transducers in such a way that the plural diffracted light of ultrasonic waves are added together by compensating the initial phase differences of the respective excited ultrasonic waves and unifying the phases.

CONSTITUTION: A multiple tilted SAW transducer (MTS) array consisting of comb-shaped transducers (DT) 41W44 of finger number 4, 5 having respectively different central frequencies and angles of inclination so as to satisfy respective Bragg conditions with respect to the conducted light is constituted. The IDTs 41W44 have the frequency characteristics of the diffraction efficiency shown by broken lines 51W54. The MTS array exhibits such a frequency characteristic of the diffraction efficiency as shown by a solid line 55 which does not fall at the crossover frequency. The diffraction efficiency is thus relatively uniform over the entire band width in which the point -3dB on the low frequency side is made 0.685GHz and the point -3dB point on the high frequency side is made 1.415GHz.