A display device may include a display panel including a gate line, a data line, and a pixel electrically connected to the gate line and the data line, where display panel displays an image based on input image data, a gate driver which outputs a gate signal to the gate line, a data driver which outputs a data voltage to the data line, and a power supply voltage generator which provides a driving voltage to the display panel, the gate driver and the data driver. The power supply voltage generator generates a gate clock signal based on an on-clock signal and an off-clock signal and changes a count value of the on-clock signal or the off-clock signal when the gate clock signal is an abnormal signal.