Area management information is cached in a cache memory by controlling the access size when an information processor accesses the area management information in an information recording medium. When the processing content of the information processor is to retrieve a free area from the area management information, a physical management block size determined from the physical characteristics of the information recording medium is used. When the processing content is to acquire a link destination from the area management information, minimum access unit of the information recording medium is used. Consequently, overhead can be lessened when the area management information is accessed.