A data processing device first reads directory data provided for each directory by a file management system which manages files using a directory structure. When meta-data to be attached to the directory data is written in proper XML format, the device appends the meta-data to the end of the read directory data, and outputs the entirety of the data obtained thereby as a directory data file. By appending the meta-data to the end of the directory data in this way, meta-data can be registered by directory with respect to existing data managed by the directory, without affecting existing applications.