Device files are disposed on respective routes through which a process accesses the same device, and access rules for those device files are unified. Foe example, where there exist two routes by which a certain process accesses a device, two device files are disposed on each of the routes. Access rules that are set for all directories that access the two device files are unified so as to permit only reading so that the device file can be accessed according to the same access rule by the two routes.