PURPOSE: To access a different kind of file which is expanded on a secondary storage device by the same system by making a user space refer to and updates the contents of a virtual area in its virtual space and then referring to and updating the contents of the file expanded on the secondary storage device.

CONSTITUTION: The contents of the file 20 expanded on the secondary storage device 2 are read in a real memory 11 by using a paging function for a virtual area; and then the user space 10 can access file data in the virtual area and the file data as the contents of the updated virtual area arm reflected on the file 20 on the secondary storage device 2. For the purpose, when the user space 10 generates a file use request call, an access environment opening module 16 expanded in a kernel acquires a virtual page of the user space 10 of the same size with the file 20 making a request, sends its address information back to the user space 10 and also generates an access table 14 in the kernel.