Abstract: A device authentication system comprises a terminal device, a data communications device connected to the terminal device, and a service provider. Device information stored in the terminal device is encrypted in order to produce authentication information. Transmission is carried out with respect to user information of the data communications device and the encrypted device information. The service provider decodes the encrypted device information using a device authentication server and identifies whether or not the terminal device is a terminal device suitable to service contents which is provided by the service provider, in accordance with the decoded device information. On the basis of an authentication result, the service provider determines whether or not the user information is transmitted to a user authentication server.