In order to add a CDC function to a ROADM system currently incompatible with CDC, without requiring any service outage, an optical communication system of the present invention includes: an optical demultiplexing unit 1-1 and 1-2 which each demultiplexes a wavelength-multiplexed optical signal inputted thereto and an optical multiplexing unit 2-1 and 2-2 which each multiplexes together some of, specifically at least two or more of, the components of the wavelength-multiplexed optical signal having been demultiplexed by the optical demultiplexing unit 1-1 or 1-2; and an optical path selection unit 3 which selectively outputs either the optical signal multiplexed by the optical multiplexing unit 2-1 or that by the optical multiplexing unit 2-2, in a form of at least two or more output optical signals.