Key switches are arranged to form plural rows, and light emitting elements
are provided in corresponding relation to the key switches. For each of
the rows, any operated key switch is detected, and, on the basis of such
detection, the light emitting elements are sequentially illuminated so
that an illuminated position reciprocates between the operated key switch
and the key switch located at a predetermined position of the row the
operated key switch belongs to. In synchronism with illumination of the
key switch located at a predetermined position of the row, at least one
of tones allocated to the row is generated. When duration of operation of
the operated key switch is greater than a predetermined time, the light
emitting elements located in a predetermined range may be illuminated in
accordance with a predetermined pattern, and an effect may be imparted to
a tone corresponding to the operated key switch.