A block processing section divides a file generated by an application into a plurality of data blocks and stored the data blocks in an auxiliary storage device. A metadata processing section stores, in the auxiliary storage device, first metadata including a hash value and information for identifying a storage location of each of the plurality of data blocks. When the file is updated, the block processing section stores an updated data block in another storage location. The metadata processing section stores, in the auxiliary storage device, second metadata including a hash value and information for identifying a storage location of each of a plurality of data blocks including the updated data block. A metadata switching section sets the second metadata to be used for file access.