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.