A computer system and file storage/read-out method. When storing data spread on a memory into a file storage unit, user .alpha.. assigns a meaningful filename-for-user, such as "sales book for April." A storage control unit converts the "sales book for April" to a meaningless filename-for-storage, such as "RST123." The correspondence between the two is stored as filename correspondence information for user .alpha. in a correspondence information storage unit. A storage processing unit stores the data with the filename "RST123." When user .alpha. is presented with a list of filenames of the stored files from a filename presentation unit, the meaningful filename of "sales book for April" is presented as the filename since a presentation control unit performs reverse conversion of the filename based on the filename correspondence information, and the meaningless filename of "RST123" is presented to other users. Security in regard to filenames can thus be secured, and inference of the file contents can be prevented.