An optical waveguide apparatus includes an optical waveguide, such as an optical sheet of a two-dimensional slab waveguide, and an appropriately-shaped plated structure provided in the optical waveguide. Typically, the plated structure is constructed so as to serve as an optical-path converting unit for optically coupling the optical waveguide and an optical device, which is to be provided on or in the vicinity of the optical waveguide, or as at least a part of a via penetrating the optical waveguide.