A wavelength checker includes an optical converter composed of a conversion material that converts infrared light into visible light. The optical converter is disposed, on an output side (side from which light is output to an external space) of a plurality of first output waveguides of an optical waveguide chip, to receive emitted light that is guided through the first output waveguides and reflected on and emitted from the light emitting-side end surface. The light emitting-side end surface is a reflection surface that is inclined to face a main substrate.