A network management system which can easily rebuild the system even when a switch in the configuration of cars occurs. A monitor apparatus including monitor cameras (1-1˜1-4, . . . ) and recording devices (1-5, . . . ) in each car (21a, 21b, . . . ) is networked. Each intra-car network is constructed as a LAN, a router (1-10 (RT1), . . . ) is connected to the LAN in each car, and an inter-car network is constructed as a WAN. The same apparatus in each car and apparatuses provided at the same positions are connected to a port of the same port number and the same LAN address is allocated to such an apparatus. As for an access from a WAN side, which apparatus is accessed is defined only by a difference in port number. Network information of the car switched car can be set merely by switching the setting of the WAN address of the router, . . . .