An information processing device that reads out and records data from and on an information recording medium includes a file system controller. File system control information is constructed in a system memory within the information processing device, and the file system controller unifies and controls a plurality of information recording media which are managed by individual file systems into a single virtual file system. In addition, the file system controller manages a priority order that indicates an information recording medium to be utilized with priority if files having the same name exist. This priority order can be changed in response to a request from an application program. Thus, the processor can unify and manage the plurality of information recording media and, also, enables the application to access all of the files having the same name.