Provided is an OLED display device that is in a black mode in which a threshold voltage of a driving TFT need not accurately be sensed. Further, a low voltage value of zero or less is constantly and continuously supplied to a data line during an initialization period, a sampling period, and a programming period in a pixel. As a result, when the pixel is driven in the black mode, a reference voltage and a data voltage having different values are not alternately supplied to the data line to minimize power consumption.