An organic light emitting display device including: an optical sensor for generating an optical sensor signal corresponding to brightness of ambient light; a first luminance control unit for providing a first luminance control signal (Vc1) for controlling a pulse width of a light emission control signal in accordance with the optical sensor signal; a second luminance control unit for providing a second luminance control signal (Vc2) for controlling the pulse width of the light emission control signal in accordance with data of one frame of the image; and a comparator/selector for comparing the first luminance control signal with the second luminance control signal and for selecting one of the first luminance control signal or the second luminance control signal for output to a scan driver.