Channel voice messages representative of a piece of music are enciphered to pieces of enciphered music data, and the pieces of enciphered music data are stored in maker exclusive messages; the maker exclusive messages are loaded into packets, and are transmitted from a server to a client; when the packets arrive at the client, the pieces of enciphered music data are restored to the channel voice messages through a reverse process so that the piece of music is produced by means of electronic musical instruments where the data restoration program has been already loaded.