A highly-convenient content duplication management system for allowing users to duplicate a content as long as the duplication is in compliance with a given usage right. In the system, a request destination device stores a content and a permitted number of duplications of the content. In response to a duplication request, the request destination device judges whether or not the request source device is an in-group device that belongs to the same group as the request destination device. When judging that the request source device is an in-group device, the request destination device transmits the content together with a permitted number that is equal to or smaller than the currently stored permitted number. The request destination device then updates the currently stored permitted number by subtracting the permitted number transmitted.