Abstract: If opening and deleting of arbitrary optical pathways are repeated in a configuration where plural OADM nodes are connected to each other in a ring manner, empty waves in the ring are fragmented, and thus, it is necessary to optimize the optical pathways. When an optical pathway is opened from an OADM node to a different OADM node, transponders capable of connecting two routes to the OADM nodes and of setting different wavelengths for two routes are mounted in a state where there are no empty waves on a part of the route, so that an already-opened optical pathway is detoured to a detour route or a different wavelength in the OADM ring, and continuous empty waves are produced in a section to be opened so as to open a new optical pathway.