An information recording medium access device for accessing an information recording medium including a nonvolatile memory, wherein said nonvolatile memory includes: a data recording area composed of a plurality of clusters, each cluster of said plurality of clusters having a unique cluster number; and a FAT (305, 306) holding a plurality of pieces of entry information serving as management information of a cluster of the data recording area, each piece of said plurality of pieces of entry information corresponding to a cluster, wherein said information recording medium access device comprises: an area management block controller; and a recording controller (16, 17), wherein said area management block controller generates area management block information comprising a plurality of area management blocks and a plurality of slots, each area management block representing a portion of the memory corresponding to a division of the FAT information into fixed length blocks, each area management block comprising a plurality of slots, each slot being a management unit for all FAT entries of clusters composing one erase block, the erase block being a minimum unit of access of the recording medium; wherein said area management block controller is configured to determine that a slot is an empty slot when the slot has entry information indicating empty clusters of a number equal to or greater than a second threshold value of clusters corresponding to entry information included in the slot, the entry information indicating whether a cluster is empty, and to determine that an area management block includes entry information indicating an area of the data recording area into which data can be written when a number of empty clusters included in all empty slots in said area management block is equal to or greater than a first threshold value, and wherein said recording controller (16, 17) is configured to write data requiring real time performance to areas of the data recording area of said nonvolatile memory corresponding to said area management blocks which have been determined as areas into which data can be written. a data recording area composed of a plurality of clusters, each cluster of said plurality of clusters having a unique cluster number; and a FAT (305, 306) holding a plurality of pieces of entry information serving as management information of a cluster of the data recording area, each piece of said plurality of pieces of entry information corresponding to a cluster, wherein said information recording medium access device comprises: an area management block controller; and a recording controller (16, 17), an area management block controller; and a recording controller (16, 17), wherein said area management block controller generates area management block information comprising a plurality of area management blocks and a plurality of slots, each area management block representing a portion of the memory corresponding to a division of the FAT information into fixed length blocks, each area management block comprising a plurality of slots, each slot being a management unit for all FAT entries of clusters composing one erase block, the erase block being a minimum unit of access of the recording medium; wherein said area management block controller is configured to determine that a slot is an empty slot when the slot has entry information indicating empty clusters of a number equal to or greater than a second threshold value of clusters corresponding to entry information included in the slot, the entry information indicating whether a cluster is empty, and to determine that an area management block includes entry information indicating an area of the data recording area into which data can be written when a number of empty clusters included in all empty slots in said area management block is equal to or greater than a first threshold value, and wherein said recording controller (16, 17) is configured to write data requiring real time performance to areas of the data recording area of said nonvolatile memory corresponding to said area management blocks which have been determined as areas into which data can be written.