To provide an OADM which is improved in reliability and reduced in cost.

An ODMX 40 demultiplexes light signals of respective wavelength components of a wavelength multiplex light signal into two by an optical coupler 41 and outputs one as a Drop signal 49 and the other as a THR signal 481. The THR signal 481 is inputted from one input terminal of a 2×1 optical SW 42 and an Add signal 50 on which a new signal is superposed is inputted from the other input terminal; and one of them is selected and outputted. Then THR signals or Add signals which are thus generated by the wavelength components are multiplexed by an OMUX 43.