A manufacturing method of an optical waveguide is disclosed, the optical waveguide transmitting an optical signal between a luminous source and an optical receiver. The optical waveguide is structured by forming a lower clad layer, a core section, and an upper clad layer one by one on a substrate; by forming a first slot and a second slot each dividing the core section from the side of the upper clad layer that is not connected to the substrate; and by forming a metal film in the first and second slots such that a first mirror and a second mirror are formed.