A communication apparatus including: a main device that has: a selection unit that selects one registration number from among provided registration numbers; a main device registration unit that transmits the registration number selected by the selection unit to an additional device and stores information to the effect that the selected registration number is used as the registration number of the additional device; a display unit that displays information; and a display control unit that causes the display unit to display information indicating which of the registration numbers is used as the registration number of the additional device based on the information stored in the main device storage section; and the additional device capable of communicating with the main device wirelessly.