Abstract: A network audio system allows AV files existing in a PC to be readily registered and music to be reproduced using a client machine. The client machine is connected to the PC and a server application and a controller application are installed in the PC. Music is reproduced using the client machine based on an AV file existing in a user folder, when the user drags and drops an icon for the AV folder to an icon for the client machine. In response to the operation, the controller application produces music piece information including the artist name and the like based the tag information of the AV file. When the music piece information is not yet registered, the server application provides the music piece information with a music piece ID for registration in the content information database. The controller application transmits a command including the ID to the client machine.