Programs for executing downloading of a program are stored in an area, i.e a non-rewritable boot area, of a rewritable flash EEPROM. Control programs for the apparatus are stored in the remaining area of the EEPROM. The programs for executing the downloading of the program, which are in the boot area, will not be lost, even if a power disconnection occurs during rewriting of the control program(s) and thus redownloading can be carried out. Information, regarding whether the downloading has failed or how far the program has been downloaded before it failed, is stored. Redownloading can be executed automatically when the power is turned on based on the stored information.