PURPOSE: To surely erase the contents of a file without introducing overload state in a computer system by detecting the operation rate of a device such as a central processing unit (CPU), and controlling the erasing of the objective file.

CONSTITUTION: Receiving information indicating that the average operation rate of respective devices is a prescribed value or lower from operation rate detecting means 1-1W1-3, a control means 2 decides that the margin of processing capacity exists in a system resource required for file erasing processing. Thereby, the control means 2 refers a control table 2-2 to detect the existence of a file to be erased. When there is the file to be erased, the control means 2 turns a file erasing means 3 to an executable state. The means 3 refers the control table 2-2 selects one file to be erased, erases the file, and informs the end of erasing to a file control means 2-1.