To obtain low insertion loss and low TTE level, a first central transducer, a second transducer and a third transducer are disposed on one surface of a piezoelectric substrate in such a manner that the second and the third transducers are in the direction of propagation (X-direction) of surface acoustic waves launched by the first transducer and the distance between center lines of the first and the second transducers and also the distance between the center lines of the first and the third transducers vary along the Y-direction perpendicular to the X-direction.