PURPOSE: To effectively utilize a filing device without increasing danger to disable the recovery of a deleted file so much concerning the deleted file managing system for erasing the file by making invalid an identifier in a correspondent file label.

CONSTITUTION: File labels 22-A to 22-D corresponding to respective files A to D contain the identifiers showing validity/invalidity and the date and time of deletion. When the size of a file to be prepared is larger than the size of an unused area in the case of preparing that file, a request discrimination control part 12 changes the deleted invalid files, which identifiers show invalidity, into the unused areas successively from the file with the oldest data and time deletion until the size of the unused area gets larger than the size of the file to be prepared, and the unused area enough for preparing the file is prepared.