PURPOSE: To perform free access and to realize easy handleability by generating and allocating a new file whose file format is changed when access is started, and releasing the file by changing a file form and storing it in an original file when the access is completed.

CONSTITUTION: A file allocation means 12 issues a file form change request to a file form changing means 16. The file form changing means 16 secures a data storage means 22 other than a data storage means 21 in which a corresponding file is stored, and stores it by changing the file form of part or all of the corresponding file. The file allocation means 12 issues a file access request to a file accessing means 17 by specifying the new file name of the data storage means 22. When the file form is different, a file releasing means 13 issues the file form changing request to the file form changing means 16 by specifying the file name and the file form.