A photovoltaic element, a light shielding portion, a planarized layer, a color filter, another planarized layer and an undercoat layer are formed successively on a semiconductor substrate, followed by forming resin lenses. A shift register includes a serial input connected to the output of the serial interface for storing bits of the digital audio signal. When presence of dead time is thus taken into consideration, a width of the timing when the zero-current switching is realized is made to be broader than a case where the presence of the dead time is not taken into consideration by the dead time. The second electrodes transmit a plurality of second input signals. With selection of those BSSID’s being no longer so constrained, it is easier to assign BSSID’s to mobile stations while allowing those mobile stations to roam among multiple AP’s. Thus, a disc substrate with little warping is obtained in a short time.