A data processor configured to perform data communication with an external device via wireless communication with a relay transmitter, comprising: a communication unit configured to perform wireless communication with the relay transmitter; a storage unit configured to store a first physical address for the relay transmitter; an authentication starter configured to, in response to the data processor being turned on, transmit, to the relay transmitter, an instruction to start authentication between the data processor and the relay transmitter along with a physical address for the data processor; an address receiver configured to receive a second physical address for the relay transmitter from the relay transmitter as a response to the instruction; a determining unit configured to make a determination as to whether the second physical address for the relay transmitter is identical to the first physical address for the relay transmitter; and a connecting unit configured to, when one or more authentication requirements are satisfied, establish wireless connection between the communication unit and the relay transmitter so as to achieve the data communication between the data processor and the external device via the relay transmitter, the authentication requirements including the determination by the determining unit that the second physical address for the relay transmitter is identical to the first physical address for the relay transmitter, characterized in that the first physical address for the relay transmitter is stored in the storage unit before the data processor is turned on, and the data processor comprises an encryption key creating unit configured to create an encryption key based on the physical address for the data processor and the first physical address for the relay transmitter, such that the created encryption key is identical to an encryption key created by the relay transmitter, wherein the communication unit is configured to perform encrypted wireless communication with the relay transmitter using the encryption key created by the encryption key creating unit, such that the instruction and the physical address for the processor which are transmitted to the relay transmitter by the authentication starter are encrypted using the encryption key created by the encryption key creating unit and such that the second physical address for the relay transmitter received by the address receiver is decrypted using the encryption key created by the encryption key creating unit. a communication unit configured to perform wireless communication with the relay transmitter; a storage unit configured to store a first physical address for the relay transmitter; an authentication starter configured to, in response to the data processor being turned on, transmit, to the relay transmitter, an instruction to start authentication between the data processor and the relay transmitter along with a physical address for the data processor; an address receiver configured to receive a second physical address for the relay transmitter from the relay transmitter as a response to the instruction; a determining unit configured to make a determination as to whether the second physical address for the relay transmitter is identical to the first physical address for the relay transmitter; and a connecting unit configured to, when one or more authentication requirements are satisfied, establish wireless connection between the communication unit and the relay transmitter so as to achieve the data communication between the data processor and the external device via the relay transmitter, the authentication requirements including the determination by the determining unit that the second physical address for the relay transmitter is identical to the first physical address for the relay transmitter, characterized in that the first physical address for the relay transmitter is stored in the storage unit before the data processor is turned on, and the data processor comprises an encryption key creating unit configured to create an encryption key based on the physical address for the data processor and the first physical address for the relay transmitter, such that the created encryption key is identical to an encryption key created by the relay transmitter, wherein the communication unit is configured to perform encrypted wireless communication with the relay transmitter using the encryption key created by the encryption key creating unit, such that the instruction and the physical address for the processor which are transmitted to the relay transmitter by the authentication starter are encrypted using the encryption key created by the encryption key creating unit and such that the second physical address for the relay transmitter received by the address receiver is decrypted using the encryption key created by the encryption key creating unit.