When the size of a file which has been read out from a magnetic disc unit less than a predetermined value, a CPU the file onto a magnetic tape of a magnetic tape unit as an archive file of a standard form to which attribute information where its size is represented by octal numeral is added. On the other hand, when the size of the file is the predetermined value or more, the CPU records such a file onto the magnetic tape as an archive file of an expanded form to which attribute information where the size of the file is represented by hexadecimal numeral and including identification symbol indicating hexadecimal representation is added. Where the attribute information of the recorded archive file does not include identification symbol, the archive file is reproduced as a standard form. Where the attribute information includes identification symbol, the archive file is reproduced as an expanded form.