To realize a data recorder and a data reproducing device capable of recording and reproducing a file based on a CPIO format even in the case of file size exceeding that of the conventional device.

When the size of the file is under a prescribed value, it is recorded in a medium as an archive file in a standard form having attribute information to display the size in octal number, the size is expressed in hexadecimal number, an archive file in an extension form having the attribute information including an identification code to express the hexadecimal number is formed and recorded in the medium when the size is equal to or more than the prescribed value. Even the file with the size exceeding that of the conventional one is recorded and reproduced based on the CPIO format since the file is reproduced as the archive file in the standard form when no identification code is included in the attribute information of the archive file recorded in the medium and is reproduced as the archive file in the extension form when the identification code is included in the attribute information of the archive file recorded in the medium.