A file server has a conversion table that stores therein, in a corresponding manner, logical addresses specified by a higher-level layer and physical addresses specified by a disk driver that are address information indicative of a storage area in a disk device. The file server accesses the disk device with a storage area indicated by a physical address as an access destination and counts up the number of access requests to each storage area in a given period of time for each of the logical addresses. The file server then updates the conversion table such that the physical addresses are lined up in a descending order of the logical addresses of a higher number of the access requests counted. Thereafter, the file server changes storage areas of data stored in the storage device based on the conversion table updated.