PURPOSE: To provide a file retaining method in an information processor for protecting an retained file before it is overwritten by changing the file name of the retained file before it is overwritten and retain it even when it is overwritten in error.

CONSTITUTION: This file retaining system is constituted of an overall controller 3 provided with a retaining step including a step for changing the file name of a retained file to a specific file name before retaining document data when a file of the same file name as that of a file for retaining document data exists in an auxiliary storage device 5 and erasing the file of the specific file name.