In a network device and a network system structuring a VLAN at the layer 2 level, a starting network device transmits a structuring packet including a port number corresponding to an address of a terminating network device and a single VLAN after having added thereto an address of the starting network device itself and a port number from which the structuring packet is outputted; a relaying network device transmits the structuring packet to which an address of the relaying network device itself, a port number to which the structuring packet has been inputted, and a port number from which the structuring packet is to be outputted are added; and a terminating network device transmits a setup packet in which port numbers are associated with the VLAN for each of the starting and the relaying network device to each of addresses of the starting and the relaying network device.