To provide a computer system that can access the identical area of a nonvolatile memory as either of a main storage area and a file area.

A memory mode processing part 111 provides processing for enabling a file on a file system to be accessed as data in a virtual memory space. A physical address calculated by a physical address calculation part 113 from a block number of a file is registered in a page table 500 in association with a virtual address acquired by a memory area acquisition part 114. Memory mode access is thus enabled. A file mode processing part 116 provides processing for saving data on a virtual memory space as a file. A block number calculated by a block number calculation part 118 from a physical address of a memory area is registered in a file management table 400. File mode access is thus enabled.