It is to realize a network management system excellent in its reliability which can prevent a wrong connection when a field wireless management station having a redundant structure is installed, and can make a backbone network redundant so as to improve a trouble resistance.In a network management system in which filed wireless management stations having gateway functions and system management functions incorporated are redundantly connected together, the plurality of field wireless management stations 11, 12 are connected to each other through a synchronizing cable 30 and synchronizing connectors Can, CNb provided in the synchronizing cable 30.