An organic light emitting display device includes a display panel which is operated in a sensing mode or display mode and is provided with a plurality of sub-pixels, wherein each sub-pixel includes a driving transistor driven in accordance with a differential voltage between data and reference voltages, and an organic light emitting diode which emits light by a current flowing in accordance with driving of the driving transistor; a first memory for storing a characteristic value of the driving transistor sensed from the sub-pixel by the sensing mode; and a panel driver for generating the reference voltage based on the characteristic value of the driving transistor for the display mode.