A personal computer connected to a USB port of a printer through a management table managing writing on an ordinary storage region in FLASH ROM recognizes the ordinary storage region in the FLASH ROM of the printer as a removable drive which is a USB mass storage class device. Accordingly, an execution file of an application program stored in a portion of the ordinary storage region in the FLASH ROM can be read with a usual access from the personal computer, enabling the application program to be executed without being installed. When the application program is executed on the personal computer, periodic accesses are made to the ordinary storage region of the printer, and when an access fails, the application program is terminated.