A clock signal synchronized with a data write signal for each scan line supplied from a light emission control circuit 4 to a scan driver 6 is supplied to an oscillator 12 generating a reference switching signal of a DC-DC converter 8 by a PWM method via a frequency divider 14. Thus, even when a ripple component by a switching operation of the converter has been superimposed on a drive voltage Va, constantly the same gate-to-source voltage Vgs is supplied to a light emission drive transistor Tr2 for each scan line, whereby a problem that a state in which light emission intensities differ for each scan line is brought about can be resolved. Further, the duty ratio of a switching signal from a PWM circuit 11 is detected by a detection circuit 13 to grasp the load condition of the converter, and when the load is light, the division ratio of the frequency divider 14 is increased to execute the switching operation at a low frequency. In this manner, the cycle (boost cycle) of the switching operation in the converter is made greater, so that a useless power loss by the switching operation in the converter can be reduced, whereby the power utilization rate of a light load time can be improved.