Abstract: Disclosed are an apparatus and a method for compensating for a fluctuation in threshold voltage due to a deterioration of a driving transistor included in pixel circuits of an OLED device. The OLED device includes a plurality of pixel circuits which are disposed at areas in which a plurality of gate lines supplying row selecting signals and a plurality of data lines supplying image signals. The individual pixel circuit includes an OLED device, a driving transistor; a switching transistor; a first capacitor; and a second capacitor, and the driving transistor applies a current corresponding to a summed voltage of a voltage charged in the first capacitor and a voltage charged in the second capacitor to the OLED, such that the OLED emits light at luminance corresponding to the current.