Optical circuit substrate

An optical circuit substrate of the present invention includes a waveguide plate and a wiring board, the waveguide plate including a substrate, an optical waveguide positioned on an upper surface of the substrate, and legs positioned on a lower surface of the substrate, the wiring board including an insulation plate, an engaging part positioned on an upper surface of the insulation plate and engaged with the legs, and an electrode positioned on the upper surface of the insulation plate to be electrically connected to an optical part. The legs of the waveguide plate are engaged with the engaging part of the wiring board, and a gap is present between a lower surface of the waveguide plate and an upper surface of the wiring board.