A piezoelectric substrate and interdigital electrode portions are covered with an insulating layer with an insulating thin film interposed therebetween. The piezoelectric substrate is made of LiTaO3 and the insulating thin film and the insulating layer are made of silicon oxide. By intentionally making the upper surface of the insulating layer flat, the deterioration of propagation efficiency of surface acoustic waves can be suppressed, so that it is possible to reduce increase in insertion loss of a resonator. Since the upper surface of the insulating layer is flat, it is also possible to reduce variation in resonant frequency and anti-resonant frequency due to the temperature change of the surface acoustic wave device.