To reduce possibility for transfer data to be diverted by providing a data transfer method, with which a desired transmission route can be selected as a transmission route in the case of transfer, and a router device for providing such a data transfer method.

In the data transfer method for a network constituted by connecting a plurality of local area networks, with which one or more router devices and terminal equipment are connected through a communication line, through the router device, a transmission route can be selected by a transmitter out of a plurality of transmission routes determined based on the peculiar address information of terminal equipment as a data transfer source and the peculiar address information of terminal equipment as a data transfer destination.