An organic light-emitting display device comprising: an organic light-emitting panel in which a plurality of pixel regions are arranged, each of the pixel regions including an organic light emission element (OLED), a drive transistor configured to drive the organic light emission element (OLED), and a sensing transistor configured to detect a threshold voltage of the drive transistor during a sensing interval, wherein the drive transistor is diode-connected by the sensing transistor during the sensing interval; a controller configured to obtain from an image signal the pixel number of a low grayscale range and the pixel number of a high grayscale range, compare the pixel number of the low grayscale range and the pixel number of the high grayscale range, wherein the low grayscale range includes grayscales of 0 through 127, and the high grayscale range includes grayscales of 128 through 255, and adjust the sensing interval according to a compared resultant; a power supplier configured to adjust a gamma reference voltage for generating a plurality of gamma voltages according to the compared resultant; a scan driver configured to apply a scan signal (Scan) to the organic light-emitting panel; a gamma voltage generator configured to generate the gamma voltages based on the adjusted gamma reference voltage (VSS'); a data driver configured to generate a data voltage (Vdata) using the gamma voltages and apply the data voltage (Vdata) to the organic light-emitting panel; an image analyzer configured to derive a histogram signal, which includes the pixel number for each grayscale, from the image signal; a calculator configured to compare the pixel number of the low grayscale range and the pixel number of the high grayscale range on the basis of the histogram signal, and generate a control signal for adjusting the sensing interval and a gamma control signal for adjusting the gamma reference voltage in accordance with a compared resultant; and a timing controller configured to generate scan control signals (SCS') for adjusting the scan signal (Scan) on the basis of the control signal, wherein if the pixel number of the high grayscale range is larger than the pixel number of the low grayscale range, the sensing interval is shortened and the gamma reference voltage is maintained as first gamma reference voltage, and wherein if the pixel number of the low grayscale range is larger than the pixel number of the high grayscale range, the sensing interval is lengthened and the gamma reference voltage becomes a second gamma reference voltage higher than the first gamma reference voltage. an organic light-emitting panel in which a plurality of pixel regions are arranged, each of the pixel regions including an organic light emission element (OLED), a drive transistor configured to drive the organic light emission element (OLED), and a sensing transistor configured to detect a threshold voltage of the drive transistor during a sensing interval, wherein the drive transistor is diode-connected by the sensing transistor during the sensing interval; a controller configured to obtain from an image signal the pixel number of a low grayscale range and the pixel number of a high grayscale range, compare the pixel number of the low grayscale range and the pixel number of the high grayscale range, wherein the low grayscale range includes grayscales of 0 through 127, and the high grayscale range includes grayscales of 128 through 255, and adjust the sensing interval according to a compared resultant; a power supplier configured to adjust a gamma reference voltage for generating a plurality of gamma voltages according to the compared resultant; a scan driver configured to apply a scan signal (Scan) to the organic light-emitting panel; a gamma voltage generator configured to generate the gamma voltages based on the adjusted gamma reference voltage (VSS'); a data driver configured to generate a data voltage (Vdata) using the gamma voltages and apply the data voltage (Vdata) to the organic light-emitting panel; an image analyzer configured to derive a histogram signal, which includes the pixel number for each grayscale, from the image signal; a calculator configured to compare the pixel number of the low grayscale range and the pixel number of the high grayscale range on the basis of the histogram signal, and generate a control signal for adjusting the sensing interval and a gamma control signal for adjusting the gamma reference voltage in accordance with a compared resultant; and a timing controller configured to generate scan control signals (SCS') for adjusting the scan signal (Scan) on the basis of the control signal, wherein if the pixel number of the high grayscale range is larger than the pixel number of the low grayscale range, the sensing interval is shortened and the gamma reference voltage is maintained as first gamma reference voltage, and wherein if the pixel number of the low grayscale range is larger than the pixel number of the high grayscale range, the sensing interval is lengthened and the gamma reference voltage becomes a second gamma reference voltage higher than the first gamma reference voltage.