A communication apparatus comprising a main device and an additional device capable of communicating with the main device wirelessly, the main device comprising: a main device storage section; a display unit for displaying information; a display control unit for causing the display unit to display registration numbers; said communication apparatus being characterized in that the main device additionally comprises: a selection unit for selecting one registration number; a main device registration unit for transmitting the registration number selected by the selection unit to the additional device; a notification unit for notifying the registration number selected by the selection unit; and a determination unit for determining whether or not the selected registration number is to be adopted by a user of the additional device upon reception of a response command from the additional device responsive to the transmission of the selected registration number by the main device registration unit and, upon determination that the selected registration number is adopted, for permitting the main device registration unit to store information indicating that the selected registration number is used as the registration number of the additional device in the main device storage section. a main device storage section; a display unit for displaying information; a display control unit for causing the display unit to display registration numbers; said communication apparatus being characterized in that the main device additionally comprises: a selection unit for selecting one registration number; a main device registration unit for transmitting the registration number selected by the selection unit to the additional device; a notification unit for notifying the registration number selected by the selection unit; and a determination unit for determining whether or not the selected registration number is to be adopted by a user of the additional device upon reception of a response command from the additional device responsive to the transmission of the selected registration number by the main device registration unit and, upon determination that the selected registration number is adopted, for permitting the main device registration unit to store information indicating that the selected registration number is used as the registration number of the additional device in the main device storage section. a selection unit for selecting one registration number; a main device registration unit for transmitting the registration number selected by the selection unit to the additional device; a notification unit for notifying the registration number selected by the selection unit; and a determination unit for determining whether or not the selected registration number is to be adopted by a user of the additional device upon reception of a response command from the additional device responsive to the transmission of the selected registration number by the main device registration unit and, upon determination that the selected registration number is adopted, for permitting the main device registration unit to store information indicating that the selected registration number is used as the registration number of the additional device in the main device storage section.