To provide a file storage technology for effectively utilizing resources while storing files without any difference between clients.

The file storage controller includes: a file storage means for tentatively storing one or a plurality of files to be stored; a file selection means for calculating the total size of the files stored in the file storage means, calculating a confidential level rate upper limit file size by multiplying the total file size and a predetermined confidential level rate, and selecting a combination of the files whose total file size is maximum without exceeding the confidential level rate upper limit file size from the files stored in the file storage means; and a storage processing means for storing the files selected by the file selection means in a data center corresponding to an index value indicating high reliability and storing the other files in a data center corresponding to an index value indicating low reliability.