To connect an electronic musical instrument and an external sound device each other by a single two-way communication means in a communicable state.

The electronic musical instrument is equipped with a general two-way communication means capable of transmitting and receiving one to a plurality of signals of different standards by one communication path simultaneously and mutually according to common communication standards, a control means of controlling transmission and reception of a musical sound control signal and an acoustic signal to and from the external sound source device including at least a sound source connected to the two-way communication means, and an acoustic output means of generating a musical sound according to the received acoustic signal. The control means transmits specified information to the external sound source device when the external sound source device is connected to the two-way communication means. Consequently, the respective signals can properly be transmitted and received between the electronic musical instrument and external sound source device which are connected by the one general two-way communication means.