One routing device which connects plural networks on which a plurality of other routing devices, including a parent router, are connected. The parent router manages network identification data to identify the plural networks. Master router data is included for each corresponding other routing device. Master router data includes master router identification data identifying whether the corresponding other routing device is a "master router" located on a path to the parent router or a "slave router" which is a routing device other than the master router, and includes network identification data identifying a network to which the corresponding other routing device connects. Upon startup of the one routing device, the master router data is acquired from the other routing devices on the networks to which the one routing device connects. It is determined whether a router function of the one routing device is enabled based on the acquired master router data.