A wavelength checker includes an optical waveguide chip. A known arrayed-waveguide diffraction grating is formed on the optical waveguide chip. The wavelength checker includes a light conversion unit made of a conversion material that converts infrared light into visible light. The light conversion unit is arranged on an output side of a plurality of first output waveguides of the optical waveguide chip to be capable of receiving light emitted from the plurality of first output waveguides. The light conversion unit is formed on a side surface of a support facing an output end surface of the optical waveguide chip. The support is fixed to a main board.