A highly efficient protection path bandwidth management method is provided. When a protection path is set up in a loop with a node A as the starting point and endpoint in order to protect a working path, the bandwidth of the protection path is changed by transferring a bandwidth change request message, containing the identifier of the protection path as well as the value of the bandwidth after the change, so as to cycle once around the protection path set up in a loop starting from a node B that first received a PATH message for a working path.