Organic light emitting display device and method for driving the same

An organic light emitting display device includes a display panel having a plurality of pixels (P), each pixel (P) connected to a data line (DL), a gate line group (GLG) and a reference line (RL), each pixel (P) further including: an organic light emitting device (OLED); a driving transistor (Tdr) controlling a current flowing in the organic light emitting device (OLED) and including first and second gate electrodes (gl, g2) overlapped with each other, with a semiconductor layer (14) provided therebetween; a first switching transistor (Tsw1) selectively supplying a data voltage supplied to the data line (DL) to a first node (n1) connected to the first gate electrode (g1); a second switching transistor (Tsw2) selectively supplying a sensing voltage to the second gate electrode (g2); a third switching transistor (Tsw3) selectively connecting a second node (n2) connected to a source electrode (s) of the driving transistor (Tdr) to the first node (n1); a fourth switching transistor (Tsw4) selectively connecting the reference line (RL) to the second node (n2); a first capacitor (C1) connected between the second gate electrode (g2) and the second node (n2), the first capacitor (C1) storing a threshold voltage of the driving transistor (Tdr); and a second capacitor (C2) connected between the first and second nodes (nl, n2), the second capacitor (C2) storing a difference voltage of the first and second nodes (nl, n2).