Abstract: A surface decoration structure includes an undercoat film, a silver mirror film layer, and a topcoat film formed on a surface of a substrate. The silver mirror film layer includes a film of stacked nanometer-sized silver particles having surfaces coated with a polymer dispersing agent, and the topcoat film includes, as a solvent, at least one member selected from the group consisting of an aliphatic hydrocarbon compound, an aliphatic hydrocarbon compound solution including 10% by mass or less of an aromatic compound, and diisobutyl ketone. The undercoat film and/or the topcoat film may include a corrosion inhibitor. The silver mirror film layer may further include a corrosion inhibitor. The surface decoration structure includes the silver mirror film layer with improved luster and corrosion resistance.

Abstract: A worm speed reducer includes a worm wheel that has an outer peripheral surface having a tooth portion formed therein, a worm shaft, and a biasing member. The worm shaft has a meshing portion that meshes with the tooth portion between a first end located adjacent to the electric motor and a second end located on the opposite side. The distance between the meshing center and the second end is larger than the distance between the meshing center and the first end. The biasing member biases the second end by use of the first end serving as a fulcrum.

Abstract: The surface roughness Ra of tooth surfaces of teeth of a worm wheel is greater than or equal to 0.1 ?m and less than or equal to 0.5 ?m and, more particularly, less than or equal to 0.3 ?m. The worm wheel is produced by forming a resin member on which the teeth are to be formed, using a resin composition that contains reinforcing fiber; forming the teeth by performing a gear-cutting process; and adjusting the surface roughness of the tooth surfaces by performing a running-in machining process on the teeth.