Abstract: An optical wavelength division multiplexing transmission system is disclosed, in which it is possible to establish a new additional line readily, without affecting lines. The optical wavelength division multiplexing transmission system has a plurality of cascaded transmission devices respectively having optical wavelength division multiplexing functions, and each of the plurality of transmission devices includes a management section for managing used and unused wavelengths, and the respective transmission devices located in a section where a new additional line is to be established allocate an unused wavelength to the new additional line, on the basis of the unused wavelength information held by the management sections, thereby ensuring a route going to the target transmission device.