A display device includes a display panel, a data driver supplying a data signal to the display panel, a gate driver supplying a gate signal to the display panel, a power supply unit supplying electric power to at least one of the display panel, the data driver, and the gate driver, a voltage monitor unit which monitors an output voltage output from the power supply unit and outputs an alarm signal when the output voltage is cut off, and a timing controller which outputs a gate control signal converting all of gate signal output from the gate driver into a gate-on voltage and a data control signal converting all of the data signal output from the data driver into a black data signal in response to the alarm signal.