Two set of filter chips on the upper and lower surfaces, each of which has a wavelength characteristic corresponding to each wavelength component of wavelength-multiplexed light, are mounted on a transparent substrate to make an optical filter element. When the wavelength-multiplexed light is inputted to the optical filter element via an optical fiber and when the same light components as those having the wavelengths demultiplexed by an optical fiber is also inputted, the demultiplexed light and the replaced wavelength-multiplexed light will be obtained at another optical fibers, respectively.