This system serves as one musical instrument by interconnecting a plurality of musical apparatuses EMa through EMf via an expandable communication connecting portion such as USB networks CB and UH. The respective musical apparatuses EMa through EMf have their own apparatus information. For the host musical apparatus EMa, a plurality of path rule information sets which are associated with a plurality of possible statuses where apparatuses are interconnected on a USB network and each of which specifies a path along which music data is transferred among the musical apparatuses are provided. Once the musical apparatuses EMb through EMf are connected to the USB network, the host musical apparatus EMa creates an actual connection pattern Pa1 representative of an actual apparatus connection status in accordance with the apparatus information of the apparatuses EMa through EMf. The host musical apparatus EMa then allows transfer of music data in accordance with a path rule information set selected on the basis of the actual connection pattern Pa1.