Light-emitting elements disposed on a light-emitting display panel are driven by constant currents, and the forward direction voltages of the light-emitting elements are obtained by a sampling/holding circuit. Then, the voltage output from a drive voltage source composed of a DC-DC converter is controlled by the forward direction voltages obtained by the sampling/holding circuit. For example, in a case in which the light emission luminance of the light-emitting display panel is changed or in other case, a sampling and holding operation is executed by the sampling/holding circuit in response to a control signal from a sampling timing control circuit at intervals shorter than ordinary intervals. With this arrangement, when light emission luminance of a light-emitting display panel is changed, the gentle changing characteristics of the light emission luminance thereof can be improved.