1. A surface acoustic wave apparatus having at least one interdigital transducer, which is disposed such that a plurality of comb-shape electrodes respectively connected to bus bars are interleaved, wherein a region with the plurality of interleaved comb-shape electrodes includes a first overlapping region with an overlapping length constant over a whole area along a propagation direction of a surface acoustic wave, and two second overlapping regions respectively formed on both sides of the first overlapping region with an overlapping length weighted in the propagation direction of the surface acoustic wave, wherein an envelope curve of the overlapping-length weighted in each of the second overlapping regions has at least two changing points in the propagation direction of the surface acoustic wave; and wherein dummy electrodes are provided except at positions corresponding to the changing points, one end of the dummy electrodes being connected to the bus bars while another end of the dummy electrodes facing corresponding ends of the plurality of comb-shaped electrodes.