PURPOSE: To prevent the secret information which remains behind in a magnetic disk device from being leaked to a third person.

CONSTITUTION: In the information processing system in which an information processor is connected to an input/output device and a magnetic disk device, and which records and fetches processing information, at the time of erasing a file on the magnetic disk device, it is prevented that the contents which remain behind on the magnetic disk device are leaked to a third person by erasing physically a record on the magnetic disk, and thereafter, eliminating the contents of the file.