An optical waveguide includes an optical waveguide main body and mirrors. The optical waveguide main body includes a first cladding layer, a second cladding layer and a core portion provided between the first cladding layer and the second cladding layer. The optical waveguide main body has a first region in which the core portion and the mirrors are arranged and the light signal is transmitted, and a second region arranged on both sides of the first region and not contributing to a transmission of a light signal. Through vias that pass through the optical waveguide main body is provided in the second region. The first region on a side that faces the light emitting element or the light receiving element is protruded larger than the second region on a side that faces the light emitting element or the light receiving element.