File storage device, the data storage method and data storage program

Extraction unit, in accordance with the format of the file requested to store in the storage means by the client device, from the file, extracts the independent enable data is data moiety stored in the storage means as a separate file. Overlap determination unit determines whether data that matches the remaining data is stored in the storage unit independently capable data from the extracted portions are extracted independently enables data or file is data that has been deleted. Storage processing section, based on the determination result of the overlap determination unit stores separate possible data or residual data does not match the data stored in the storage means in the storage means. Restoring portion, in response to the request from the client device, storing unit is restored to the file by combining the independent enable data and remaining data stored in the storage means.