Attenuation is an essential characteristic of wave propagation, however, the quantitative measurement of bulk waves is not easy by the conventional immersion ultrasonic method because the diffraction and reflection losses are much higher [1] than the attenuation for common metals. Therefore we require samples of perfectly parallel and flat surfaces for this measurement. On the contrary, the attenuation of the leaky Rayleigh wave which propagates on the water/solid interface is noticeable [2–4] because of the energy leak from the solid surface into water. Thus the attenuation measurement of the leaky Rayleigh wave is relatively easy.