An organic light emitting display device includes a display panel including a plurality of pixels having an organic light emitting diode and a pixel circuit; a gate driver to supply the plurality of pixels with a scan signal, a sensing signal, and a driving voltage; a data driver to supply data voltages and a reference voltage to the plurality of pixels in a driving mode, and sense voltages charged into the plurality of pixels in a sensing mode; a discharging driving unit to initialize voltages of a plurality of sensing power lines when the display device switches from the driving mode to the sensing mode; a timing controller to control the gate driver, the data driver, and the discharging driving unit to operate in and switch between the driving mode and the sensing mode; and a memory to store compensation data for the plurality of pixels.