Abstract: According to some aspects of the disclosure, an organic light-emitting display device including a display panel including a driving thin film transistor (TFT), comprises a sensing unit configured to perform a sensing operation for external compensation of the display panel, and an analog-digital converter (ADC) configured to perform a conversion operation of converting an analog value held in the sensing unit into a digital value, wherein the sensing unit comprises a basic sensing unit configured to perform a sensing operation on the driving TFT, and a dummy sensing unit configured to perform a sensing operation on changes in a gain and an offset of the ADC, and the basic sensing unit and the dummy sensing unit are in a cascade connection to each other.