One recording medium accessed from a plurality of applications is generally divided into a plurality of regions. When partitions are used to control this region dividing, the sizes of the partitions are hard to change to thereby prevent an effective use of a recording medium. A recording medium is divided into a plurality of regions, and an unused area in each region is written with dummy data that can be overwritten only by a specific application or a specific file, thereby making easy the division into a plurality of regions and a change in size.
