Abstract: In an optical concentrator a plurality of ports are provided for inputting and outputting first and second optical signals having different wavelength regions. An optical coupler is connected to each of the plurality of ports without being through remaining ones of the plurality of ports. The optical coupler transmits the second optical signal input from one of the plurality of ports to at least one of the remaining ports. A transmitter is provided to connect the plurality of ports in a loop form. The first optical signal input from each port is transmitted from the transmitter. Demultiplexers are arranged at each port for demultiplexing the first and second optical signals input from each port so as to guide the first optical signal to the transmitter and the second optical signal to the optical coupler.