A bus system interconnects a plurality of devices of various categories constituting an electronic music instrument apparatus for exchanging signals among the devices having unique addresses. The bus system has a serial clock line for transmission of a clock signal, and a serial data line for transfer of a data signal from a source device to a destination device in synchronization with the clock signal. The source device operates as a master to commence a communicating session such as to send the clock signal to the serial clock line and to send the data signal to the serial data line in synchronization with the clock signal. The destination device operates as a slave so as to receive the data signal based on the clock signal. The source device formulates the data signal containing a unique address specifying the destination device such that the destination device can receive the data signal exclusively from the source device. The unique address contains category information designating a category to which the destination device belongs and a sub-address specifying the destination device in the designated category.