In a pixel circuit formed by using a MOS process, a constant current is applied from a second transistor (T2) as a constant current source to an organic EL device coupled to a third transistor (T3) so that the organic EL device emits light, during the period when the third transistor (T3) is in the conductive state. The third transistor (T3) is switched on and off based on its gate voltage dependent upon a signal value written to a capacitor (Cs) and a ramp signal voltage (Vcs). Thus, the organic EL device emits light during the period dependent upon the signal value. That is, displaying operation is implemented with gray-scale being controlled according to a video signal value.