To generate a bulk wave at VHF, UHF bands with an excellent generating efficiency used for a semiconductor cleaner by stimulating a bulk wave in a thickness longitudinal group so as to emit the bulk wave in the thickness direction of a piezoelectric flat plate.

An interdigital electrode(IDT) 101 is formed by arranging in parallel lots of pairs of electrode fingers having positive and negative electric polarity through the use of a metallic conductor made of an aluminum or the like to the surface of a piezoelectric flat plate 100. Furthermore, reflectors 102, 103 made of a metallic conductor are formed to both sides of the IDT 101. Then an AC voltage is applied to the IDT 101 to cause resonance in the SAW resonator. Then a medium such as liquid is arranged to a rear side of the piezoelectric substrate 100, that is, in contact with the bottom, then a bulk wave is emitted into a medium as an ultrasonic wave. Furthermore, in the case of using a basic building block consisting of the interdigital electrode 101 and a couple of the reflectors 102, 103 for an ultrasonic wave transducer, a difference of mass between the positive and negative electrode fingers of the IDT 101 is selected to be 10% or over and 50% or below.