To provide a means which can shorten a rewrite operation time when a flash ROM is abnormally terminated during writing because of failures of a power source, a communication means, etc.

This apparatus is provided with an EEPROM 107, dividing a program data to be written to an optimum size, sequentially writing a transfer data sent from a host to a flash ROM 108, storing a data block number and a division size of the transfer data in the EEPROM 107 and storing a code indicating an end in the EEPROM 107 when all the transfer data is completely processed and written. Accordingly only a part not written and a part changed can be written at a rewrite time.