When transmission volume declines due to adaptive modulation, a substitute path is set, without affecting signal continuity, upon a data transmission path whereupon communications bandwidth cannot be secured. Provided is a bandwidth guaranteeing protocol comprising a first wireless node means that sets an adaptive modulation switching margin of a predetermined range for Quality of Service that is a condition for the execution of adaptive modulation that reduces communications bandwidth when the Quality of Service of an MPLS network wireless zone degrades, and instructs an initiator node that sets an LSP to reserve bandwidth for a substitute LSP for an LSP that is set upon the wireless zone and requires restoration, as well as instructing the initiator node to switch to the substitute LSP, prior to executing adaptive modulation within the adaptive modulation switching margin; and a second wireless node means that is the initiator node, which executes the reservation of the substitute LSP bandwidth and the switching to the substitute LSP in response to the instruction issued by the first wireless node device, and cuts off the LSP that has been switched to the substitute LSP.