An organic light emitting display device comprising: a display panel including a plurality of pixels, which are respectively formed in a plurality of pixel areas defined by crossings of a plurality of gate lines (GL to GLm) and a plurality of data lines (DL1 to DLn), a plurality of sensing lines (SL1 to SLn), and a plurality of second gate voltage lines (TGL1 to TGLn) connected to the plurality of pixels, wherein each of the plurality of pixels includes at least one transistor including first and second gate electrodes (111 and 117) which overlap each other with a semiconductor layer therebetween; a panel driver to drive the display panel in a display mode or a sensing mode, to sense a threshold voltage of the at least one transistor included in each of the plurality of pixels through the plurality of sensing lines (SL1 to SLn) to generate a sensing data (Sdata) in the sensing mode, and generate a second gate voltage data (Tdata) based on the sensing data (Sdata) of each pixel in the display mode; and a voltage supply unit to generate a second gate electrode voltage (Vtg) corresponding to the second gate voltage data (Tdata) supplied from the panel driver, and apply the second gate electrode voltage (Vtg) to the second gate electrode of the at least one transistor, included in each pixel, through a corresponding second gate voltage line, wherein the plurality of second gate voltage lines (TGL1 to TGLn) are grouped into a plurality of groups (TGLG-1 to TGLG-k), wherein the display panel further comprises a plurality of second gate voltage common lines (TGCL-1 to TGCL-k) connected in common to a plurality of second gate voltage lines (TGL1 to TGLn) included in each of the plurality of groups (TGLG-1 to TGLG-k), wherein: the panel driver is configured to correct input data of each pixel to correction data (DATA) through data correction based on the sensing data (Sdata) of each pixel, and displays the correction data (DATA) in each pixel; the panel driver is configured to detect a threshold voltage shift of the at least one transistor from the sensing data (Sdata), and when the detected threshold voltage shift of the at least one transistor is equal to or greater than a certain voltage, the panel driver is configured to generate the second gate voltage data (Vtg) for restoring the threshold voltage shift of the at least one transistor to a threshold voltage shift which is less than the certain voltage, wherein when the threshold voltage shift is equal to or greater than the certain voltage, the threshold voltage shift cannot be compensated for through data correction alone. a display panel including a plurality of pixels, which are respectively formed in a plurality of pixel areas defined by crossings of a plurality of gate lines (GL to GLm) and a plurality of data lines (DL1 to DLn), a plurality of sensing lines (SL1 to SLn), and a plurality of second gate voltage lines (TGL1 to TGLn) connected to the plurality of pixels, wherein each of the plurality of pixels includes at least one transistor including first and second gate electrodes (111 and 117) which overlap each other with a semiconductor layer therebetween; a panel driver to drive the display panel in a display mode or a sensing mode, to sense a threshold voltage of the at least one transistor included in each of the plurality of pixels through the plurality of sensing lines (SL1 to SLn) to generate a sensing data (Sdata) in the sensing mode, and generate a second gate voltage data (Tdata) based on the sensing data (Sdata) of each pixel in the display mode; and a voltage supply unit to generate a second gate electrode voltage (Vtg) corresponding to the second gate voltage data (Tdata) supplied from the panel driver, and apply the second gate electrode voltage (Vtg) to the second gate electrode of the at least one transistor, included in each pixel, through a corresponding second gate voltage line, wherein the plurality of second gate voltage lines (TGL1 to TGLn) are grouped into a plurality of groups (TGLG-1 to TGLG-k), wherein the display panel further comprises a plurality of second gate voltage common lines (TGCL-1 to TGCL-k) connected in common to a plurality of second gate voltage lines (TGL1 to TGLn) included in each of the plurality of groups (TGLG-1 to TGLG-k), the panel driver is configured to correct input data of each pixel to correction data (DATA) through data correction based on the sensing data (Sdata) of each pixel, and displays the correction data (DATA) in each pixel; the panel driver is configured to detect a threshold voltage shift of the at least one transistor from the sensing data (Sdata), and when the detected threshold voltage shift of the at least one transistor is equal to or greater than a certain voltage, the panel driver is configured to generate the second gate voltage data (Vtg) for restoring the threshold voltage shift of the at least one transistor to a threshold voltage shift which is less than the certain voltage, wherein when the threshold voltage shift is equal to or greater than the certain voltage, the threshold voltage shift cannot be compensated for through data correction alone.