To impart hitless characteristics to an optical multiplexer/demultiplexer, and at the same time, to switch a tuned wavelength at high speed.

When two optical multiplexer/demultiplexers capable of switching the tuned wavelength at high speed but not hitless are used, the demultiplexing terminal of a first optical multiplexer/demultiplexer and the input terminal of a second optical multiplexer/demultiplexer are connected, and a multiplexing terminal of the first optical multiplexer/demultiplexer and an output terminal of the second optical multiplexer/demultiplexer are connected. Signal light from a first wavelength multiplexing optical demultiplexing terminal is connected to the light input terminal of a second wavelength multiplexing multiplexer/demultiplexer. The light signal from the light output terminal of the second wavelength multiplexing multiplexer/demultiplexer is connected to a light multiplexing/demultiplexing terminal of the first wavelength multiplexing multiplexer/demultiplexer. The no-interference wavelength multiplexer/demultiplexer has a mechanism for executing the respective wavelength selection control of the first wavelength multiplexing multiplexer/demultiplexer and the second wavelength multiplexing multiplexer/demultiplexer.