To provide a surface acoustic wave device which uses leakage surface acoustic waves, and is capable of increasing a sound speed and easily achieving a frequency increase.

In the surface acoustic wave device 1, an IDT electrode 3 is formed on an LiNbO3 substrate 2, a silicon oxide film 6 is formed so as to cover the IDT electrode 3 on the LiNbO3 substrate 2, and a dielectric layer 7 is formed on the silicon oxide film 6. The transverse wave speed of the dielectric layer 7 is higher than a slow transverse wave velocity in LiNbO3, and when the film thickness of the dielectric layer 7 is defined as H3, a normalized film thickness H3/λ normalized by the wavelength λ of the leakage surface acoustic waves lies in the range of 0.25-0.6.