A communication device for an electronic musical instrument for transmitting and receiving various kinds of electronic information in the electronic musical instrument between the electronic musical instrument and an other electronic instrument using a musical instrument digital interface (MIDI) signal form, the communication device comprising: a battery (B); an input terminal that is connected to a MIDI output terminal of the electronic musical instrument ; an output terminal that is connected to a MIDI input terminal of the electronic musical instrument ; and a control unit that transmits and receives various kinds of electronic information between the electronic musical instrument and the other electronic instrument via the input terminal and the output terminal ; the communication device being characterized in further comprising: a switching unit that switches taking in electric power to be supplied to the control unit in accordance with a communication state of the control unit in a following manner: in a case when no various kinds of electronic information is received and transmitted between the electronic musical instrument and the other electronic instrument, the switching unit switches taking in the electric power to be supplied to the control unit through a MIDI signal line from the electronic musical instrument via the input terminal ; and in a case when electronic information is received or transmitted between the electronic musical instrument and the other electronic instrument, the switching unit switches taking in the electric power from the battery (B). a battery (B); an input terminal that is connected to a MIDI output terminal of the electronic musical instrument ; an output terminal that is connected to a MIDI input terminal of the electronic musical instrument ; and a control unit that transmits and receives various kinds of electronic information between the electronic musical instrument and the other electronic instrument via the input terminal and the output terminal ; the communication device being characterized in further comprising: a switching unit that switches taking in electric power to be supplied to the control unit in accordance with a communication state of the control unit in a following manner: in a case when no various kinds of electronic information is received and transmitted between the electronic musical instrument and the other electronic instrument, the switching unit switches taking in the electric power to be supplied to the control unit through a MIDI signal line from the electronic musical instrument via the input terminal ; and in a case when electronic information is received or transmitted between the electronic musical instrument and the other electronic instrument, the switching unit switches taking in the electric power from the battery (B). in a case when no various kinds of electronic information is received and transmitted between the electronic musical instrument and the other electronic instrument, the switching unit switches taking in the electric power to be supplied to the control unit through a MIDI signal line from the electronic musical instrument via the input terminal ; and in a case when electronic information is received or transmitted between the electronic musical instrument and the other electronic instrument, the switching unit switches taking in the electric power from the battery (B). <EOS>