FIG. 7 is a graph showing the electromechanical coefficient KR 2 of Rayleigh waves as a function of the Euler angle ?? when IDT electrodes that are made of Al and have a normalized film thickness of about 8% are produced with grooves provided in LiNbO3 substrates with Euler angles (0???, ??, 0???), and SiO2 layers with various film thickness are formed on the substrates.