PURPOSE: To prevent short-circuit between electrode digits and to facilitate the manufacture by forming selectively a metal oxide only to a side ridge of the electrode digit in the manufacture process of a converter.

CONSTITUTION: Electrode digits 4, 5 of a couple of IDT electrodes, a reflection slit 6 along a propagation direction of a surface acoustic wave are arranged alternately at an electrode digit width and gap of λ/4 basically on the surface of a piezoelectric substrate 1. In order to prevent occurrence of short-circuit between electrode digit, oxidation or anodic oxidation is applied to side parts of a half of the electrode digits 4 and the slits 6 to obtain a metal oxide 7. At the manufacture of the converter, a metallic film 19 is adhered to the entire surface of the substrate 1, covered with a photoresist 20, exposed via a mask 21, a surface exposed part of the film 19 is removed after the development to form the metallic oxide 7 to the side ridge of the film 19 under the remaining resist 20, the metallic film 22 is adhered entirely by using the resist 20 as a mask and the remaining resist 20 is removed together with the film 22 adhered to the surface.