A reception intensity measuring unit measures a reception intensity of a radio wave received by a radio reception unit under control of a connection control unit. When it is judged that the reception intensity of the received radio wave is larger than a reception intensity set in advance, the reception intensity measuring unit controls a transmission intensity changing unit to lower a transmission intensity of a radio wave to be transmitted from a radio transmission unit. When the transmission intensity of the radio wave to be transmitted from the radio transmission unit is lowered by the transmission intensity changing unit, an authentication processing unit executes authentication processing with another apparatus via the radio reception unit and the radio transmission unit and controls an authentication data registering unit to register authentication data, which is obtained as a result of the authentication processing, in a memory.