PURPOSE: To prevent dimensions in the longitudinal direction of a substrate from enlarging even for a longer delay time, by providing a reflective propagation path converter to reflect an incident surface acoustic wave at 180° and separating the transmission path of the reflected surface acoustic wave the propagation path of the incident surface acoustic wave from each other.

CONSTITUTION: The surface wave radiated from a reed-screen type electrode 12 for input is reflected by a reflective grid 14 and is reflected again by a reflective grid 15 and reaches a reflective propagation path converter consisting of multistrip couplers 18, 19 and 20. The surface wave reflected at 180° by the reflective propagation path converter is propagated in a reflective grid 16 through a propagation path different from that for the incident surface wave and is reflected there and is reflected again by a reflective grid 17 and reaches a reed-screen type electrode 13 for output. An absorber 21 for absorbing the surface wave is coated on the part between reflective grids 15 and 16 to prevent the surface wave, which is reflected by reflective grids, from reaching the reflective grid 17 directly.