a trunk link 5 the communication apparatuses 2 and 3 are connected by a trunk link 6 the communication apparatuses 3 and 4 are connected by a trunk link 7 a management apparatus 10 and apparatuses 11 to 13 which are connected to the vlan 1 setting ports are connected to the communication apparatus 1 apparatuses 14 to 16 which are connected to the vlan 1 setting ports are connected to the communication apparatus 2 a management apparatus 20 and apparatuses 21 to 23 which are connected to the vlan 2 setting ports are connected to the communication apparatus 3 a management apparatus 30 and apparatuses 31 to 33 which are connected to the vlan 3 setting ports are connected to the communication apparatus 4 the communication apparatuses 1 to 4 each include a plurality of connection ports the communication apparatuses 1 to 4 can perform vlan settings by using vlan numbers set for the connection ports a specific example of the network system is a system in which in a train formation a communication apparatus in provided in each car and communication is performed among the cars by connecting the cars through trunk links however the network system is not limited to such communication among the cars fig2.