A dielectric waveguide includes a dielectric of a rectangular parallelepiped in shape, an input/output electrode formed on a first face of the dielectric, and a conductor film formed on an outer face of the dielectric. The input/output electrode extends from a first end which is a vertex or a neighborhood of the vertex of a first face (bottom face) of the dielectric inward on the bottom face; and environs along both sides and the first end of the input/output electrode include a conductor-unformed section in which there is no conductor film.