To establish an alternative path without giving an influence on signal continuity to a data transmission line to which a communication bandwidth cannot be secured any more when the transmission capacity decreased by adaptive modulation.It includes a first radio node means which sets an adaptive modulation changeover margin having a predetermined width to communication quality for a trigger of performing adaptive modulation which decreases a communication bandwidth when the communication quality of a radio transmission channel section has deteriorated, and prior to performing the adaptive modulation, in the adaptive modulation changeover margin, instructs an initiator node which has established an LSP in the radio transmission channel section to reserve a bandwidth of an alternative LSP for the LSP which requires restoration of diverting to an alternative path and to change over to the alternative LSP; and a second radio node means which is the initiator node, and according to the instructions from the first radio node means, reserves a bandwidth of the alternative LSP, performs changeover to the alternative LSP and disconnects the LSP which has been changed over to the alternative LSP.