To provide a radio LAN system, which can receive communication services without using a specific domain.

A radio terminal device 6 has an ID different from the relevant domain ID (ESSID: Extended Service Set ID) and sends this ID to a device 2 equipped with a LAN function, along with a connection request. The device 2 equipped with a LAN function collates the sent ID with an ID stored in the device. If the sent ID coincides with the stored ID, connection is granted for the radio terminal device 6, and preparation for specific data communication is conducted. If the sent ID does not coincide with the stored ID, connection is rejected. Namely, suitability for connection is decided based on consistency/ inconsistency of the ID, which is set in addition to the domain ID.