A dielectric device comprises a substrate made of a metal and an oxide dielectric layer mounted on a surface of the substrate. The surface of the substrate has metal oxide regions distributed like islands, while the oxide dielectric layer is in close contact with the substrate through the metal oxide regions. Since adhesion is higher in an area where the substrate and the oxide dielectric layer are in close contact with each other through the metal oxide regions distributed like islands on the surface of the substrate, the adhesion between the substrate and oxide dielectric layer in the dielectric device is enhanced. As compared with a case where a rough surface is formed on a metal foil, the metal oxide region and the substrate are inhibited from forming a rough surface, whereby leakage characteristics can be kept from being deteriorated by the rough surface.