The pixel circuit which controls the driving of the organic light emitting diode includes a driving TFT which supplies a driving current to the organic light emitting diode; a sampling TFT which samples a threshold voltage of the driving TFT; a first initializing TFT which supplies an initialization voltage to one electrode of the organic light emitting diode; and a storage capacitor which stores a voltage applied to the driving TFT, and at least one of the driving TFT, the sampling TFT, and the first initializing TFT includes a shielding electrode disposed between the substrate and the active layer. Therefore, even though the external light is irradiated onto a transparent substrate, a full white gray-level and a full black gray-level can be expressed so that the gray-level expressiveness may not be degraded.