An electronic piano is controllable with a remote controller; since the remote controller is physically separated from the electronic piano, users are liable to mislay the remote controller somewhere around the electronic piano; in this situation, the user instructs the electronic piano to transmit a radio wave representative of inquiry, and the missing remote controller responds to the inquiry by transmitting a radio wave representative of annunciation; the electronic piano is equipped with antennas separated from each other on the piano cabinet, and the received power at the antennas is varied depending upon the location of the missing remote controller; the electronic piano analyzes the received power so as to notify the user of the possible location of the missing remote controller.