An optical cross-connect system is provided with M fixed wavelength light sources and external modulators corresponding to respective optical paths, serving as light sources for wavelength conversion devices corresponded to M x N optical paths. By means of electrical signals for the converted optical signals canied on the M x N optical paths, CW lights input to the external modulators from the respective light sources are modulated, wavelength converted and then output. Accompanying this wavelength conversion, wavelength multiplexed light sources which can select lights from a plurality of fixed wavelength light sources and output to predetermined output ports, are used for the light sources of the plurality of wavelength conversion devices of the cross-connect system. In this way, the light sources of a plurality of wavelength conversion sections are commonalized using a fixed wavelength light source. As a result wavelength multiplexed light sources which can respectively output lights of optional wavelengths to a plurality of output ports using a plurality of fixed wavelength light sources are realized. Moreover, by using such wavelength division multiplexed communication light sources, then a highly realizable and economical optical cross-connect system is possible.