As a wavelength selection filter, a filter in which dielectric multilayered films are formed on a substrate, an optical fiber grating in which diffraction grating is formed in an optical fiber, and so on, can be used. As another optical demultiplexer 33, as described in Japanese Patent No. 2599876, an arrayed optical waveguide diffraction grating which forms plural optical waveguides having different length of optical paths on the substrate to demultiplex the multiple wavelength light to the respective wavelengths can be used.