The invention provides a data driver. The data driver includes an input unit configured to receive data from outside, a digital-analog converter configured to generate a data signal by using the data,a data comparator configured to compare a reference gray scale value with the data and to generate a first control signal or a second control signal corresponding to a comparison result, and an output unit configured to supply the data signal to data lines, wherein the output unit includes at least one buffer, and a slew rate of the at least one buffer is set to vary depending on whether the first control signal or the second control signal is generated.