A surface acoustic wave device has a piezoelectric substrate 1, and a comb transducer 2 formed on a surface of the piezoelectric substrate 1. Grooves 5 for eliminating an unnecessary wave are formed in a back surface of the surface acoustic wave device in such a manner that the interval of the adjoining grooves 5 is decreased as the groove 5 extends from one end 7 of the piezoelectric substrate 1 to the other end 8 thereof. With this arrangement, angles defined by the extending directions of the respective grooves 5 and the propagating direction of the surface acoustic wave can be differentiated from each other, and the reflecting conditions of the unnecessary wave to the respective grooves 5 can be varied from each other. This arrangement enables to improve characteristics of the surface acoustic wave device.