Tone generation control signal and sound signal are communicated between an electronic musical instrument and an external apparatus, using a communication interface capable of bidirectionally communicating one or more types of signals via a common communication path in accordance with a common communication standard. Thus, where the electronic musical instrument does not have its own internal tone generator while the external apparatus has its own tone generator, a sound signal of a tone, corresponding to the tone generation control signal output from the electronic musical instrument, can be generated by the external apparatus and supplied to the electronic musical instrument, so that the electronic musical instrument can sound the sound signal. Also, information of the electronic musical instrument is transmitted to the external apparatus so that input and output paths to and from the tone generator of the external apparatus can be automatically set, via the communication interface tom, in correspondence with the electronic musical instrument.