A network system includes a master device (200), a plurality of slave devices; and a hub device including a plurality of ports on a downstream side. The master device (200) includes: a storage unit (204) in which setting information is stored, information on a device and topological information being set in the setting information; a real configuration information generating unit (202) that generates real configuration information including information on the device constituting an actual network system and topological information on the device; and a determination unit (203) that determines whether a destination of each device is correct by comparing the real configuration information to the setting information. The determination unit (203) determines that the destination of the slave device is correct, even if a position of the connected port is incorrect with respect to the slave device connected to the hub device.