an N×N wavelength path establishment circuit having N input ports and N output ports, N being an integer of at least 2, outputting light input from an input port to a different output port depending on the wavelength of the input light, and the wavelength of light output from an output port being different depending on the input port;

n communication nodes, n being an integer at least 2 and not greater than N, for outputting information of an input optical signal, as is or after changing a part of the information, as an optical signal of a predetermined wavelength; and

optical waveguides for connecting the input ports and the output ports of the N×N wavelength path establishment circuit, and the communication nodes,

wherein for at least some of the n communication nodes, in order to form a first logical-ring transmission path where an optical signal transmitted from one communication node circulates in a clockwise direction and returns to the one communication node via other communication nodes or to form both the first logical-ring transmission path and a second logical-ring transmission path where an optical signal transmitted from the one communication node circulates in a counterclockwise direction and returns to the one communication node via the other communication nodes, a correlation of wavelengths for connecting between the input ports and the output ports of the N×N wavelength path establishment circuit, wavelengths of optical signals output from the respective communication nodes, and connections between the input ports and the output ports of the N×N wavelength path establishment circuit, and the respective communication nodes are set.