In a plurality of rooms, hubs are installed to build a star-shaped LAN, and tone-generation-related devices, such as a keyboard, tone generator device and speaker, are connected to the respective hubs. For example, in an internal network, the keyboard is logically connected to an input side of the tone generator device and a speaker is connected to an output side of the tone generator device, so as to build a tone generation system. The tone-generation-related devices are provided with respective network adaptors so that they can be readily connected to the LAN. Communication is carried out between the tone-generation-related devices, using a communication protocol intended for retransmission control. Each of the tone-generation-related devices is in the form of a processor device, which executes a program corresponding to a function of a desired processing element to thereby implement the desired processing element. Once a given tone-generation-related device, implementing a plurality of processing elements, is connected to the network, an internal connection between the processing elements is canceled.