An organic light emitting display device includes a display panel having a plurality of pixels, each pixel connected to a data line, a gate line group and a reference line, each pixel further including: an organic light emitting device; a driving transistor controlling a current flowing in the organic light emitting device and including first and second gate electrodes overlapped with each other, with a semiconductor layer provided therebetween; a first switching transistor selectively supplying a data voltage supplied to the data line to a first node connected to the first gate electrode; a second switching transistor selectively supplying a sensing voltage to the second gate electrode; a third switching transistor selectively connecting a second node connected to a source electrode of the driving transistor to the first node; a fourth switching transistor selectively connecting the reference line to the second node; a first capacitor connected between the second gate electrode and the second node, the first capacitor storing a threshold voltage of the driving transistor; and a second capacitor connected between the first and second nodes, the second capacitor storing a difference voltage of the first and second nodes.