PURPOSE: To obtain a satisfactory operation by a small number of wirings by changing the direction of a current of light emitting elements corresponding to two keys and allowing them to emit a light beam separately.

CONSTITUTION: Light emitting diodes related to the same sound name belonging to each octave are connected in parallel, and two pieces of light emitting diodes 101 and 102, 103 and 104,... related to keys of adjacent sound names in the same octave, for instance, C and D, D and E... are connected in parallel, respectively. In this case, two pieces of adjacent light emitting diodes are connected in parallel to each other so that the direction in which a current flows becomes a reverse direction, by which only one of them is allowed to emit a light beam in accordance with the direction in which a current flows to this parallel circuit from the outside.