Original data and derivative data are managed securely and conveniently. A processing unit of a computer 1 whose IP address is J1 sends a file A as a file A1 to a Web server (whose URL is URL-100) of another computer 100, via the Internet. A file management unit generates accompanying information comprising link information "file A1, URL-100" and processing content information "copying" for the file A, and generates accompanying information comprising link information "file A, IP address J1" and processing content information "copied from file A" for the file A1. An attachment unit attaches the accompanying information to the files A and A1.