Abstract: A printer receives a data card and an interface card as function extension cards. The printer has at least one card slot receiving a data card storing image data and/or a specific execution file and an interface card for data communication with an external apparatus. A detection unit detects whether a memory card installed in the card slot is the data card or the interface card, and a control unit determines whether to execute the interface card, if the interface card is installed in the card slot according to the detection unit, to communicate with the external apparatus. Accordingly, the function extension cards allow mutual data communication between the printer and various external apparatuses having various interfaces, and also new functions not supported by the printer can be added.