A three-dimensional optical waveguide is formed by laminating planar substrates such as a plurality of lens substrates and, an isolator substrate and a wavelength division multiplexing filter, the optical substrates at least include a waveguide substrate having a waveguide and a reflecting surface. In the three-dimensional optical waveguide, the planar substrates are positioned by markers integrally formed on at least two of the planar substrates. Light directed into the waveguide is reflected by a reflecting surface and passes through the lens substrates and the isolator substrate.