A memory controller, comprising: memory control means configured to access a readable/writable nonvolatile memory and configured to read and write data on the basis of a sector unit of a file system established for the nonvolatile memory, the memory controller being characterized by comprising: a data storage that temporarily stores an address conversion table in which one or multiple records, each comprising a sector number of a sector constituting a given file stored on the nonvolatile memory and a physical address on the nonvolatile memory corresponding to the sector number, are registered for each given file; memory allocation means configured to allocate a memory region on the data storage for the address conversion table corresponding to a file when a request is made to open the file from an external source; memory release means configured to release the memory region allocated by the memory allocation means at a given time; and sector number storing means configured to store in sequence sector numbers of at least some of sectors constituting the file in each record of the address conversion table for which the memory region is allocated and configured to notify the memory control means accordingly after the storing, wherein: the memory control means searches the nonvolatile memory to acquire the physical address corresponding to the sector number in the each record of the address conversion table and stores each acquired physical address in the corresponding record upon receiving the notification from the sector number storing means, and makes reference to the address conversion table corresponding to the file using the sector number of the sector as a key to acquire the physical address corresponding to the sector in accessing the sector constituting the file. memory control means configured to access a readable/writable nonvolatile memory and configured to read and write data on the basis of a sector unit of a file system established for the nonvolatile memory, the memory controller being characterized by comprising: a data storage that temporarily stores an address conversion table in which one or multiple records, each comprising a sector number of a sector constituting a given file stored on the nonvolatile memory and a physical address on the nonvolatile memory corresponding to the sector number, are registered for each given file; memory allocation means configured to allocate a memory region on the data storage for the address conversion table corresponding to a file when a request is made to open the file from an external source; memory release means configured to release the memory region allocated by the memory allocation means at a given time; and sector number storing means configured to store in sequence sector numbers of at least some of sectors constituting the file in each record of the address conversion table for which the memory region is allocated and configured to notify the memory control means accordingly after the storing, wherein: the memory control means searches the nonvolatile memory to acquire the physical address corresponding to the sector number in the each record of the address conversion table and stores each acquired physical address in the corresponding record upon receiving the notification from the sector number storing means, and makes reference to the address conversion table corresponding to the file using the sector number of the sector as a key to acquire the physical address corresponding to the sector in accessing the sector constituting the file. a data storage that temporarily stores an address conversion table in which one or multiple records, each comprising a sector number of a sector constituting a given file stored on the nonvolatile memory and a physical address on the nonvolatile memory corresponding to the sector number, are registered for each given file; memory allocation means configured to allocate a memory region on the data storage for the address conversion table corresponding to a file when a request is made to open the file from an external source; memory release means configured to release the memory region allocated by the memory allocation means at a given time; and sector number storing means configured to store in sequence sector numbers of at least some of sectors constituting the file in each record of the address conversion table for which the memory region is allocated and configured to notify the memory control means accordingly after the storing, wherein: the memory control means searches the nonvolatile memory to acquire the physical address corresponding to the sector number in the each record of the address conversion table and stores each acquired physical address in the corresponding record upon receiving the notification from the sector number storing means, and makes reference to the address conversion table corresponding to the file using the sector number of the sector as a key to acquire the physical address corresponding to the sector in accessing the sector constituting the file.