A display device comprising: a display panel configured to display an image; a driver including a data driver for driving the display panel; a power supply unit configured to supply an output voltage (Vout); and a timing controller configured to control the driver, wherein the power supply unit is configured to vary the output voltage (Vout) corresponding to a variation of a load for compensating a voltage variation caused by the variation of the load, before the load is changed; characterised in that the power supply unit 180 comprises a current amount analyzing unit, a variation amount determining unit, and an output voltage varying unit, and is configured to receive a data signal (DATA) from the timing controller or the data driver, and is configured to receive a timing signal (Sync, DDC) from the timing controller or the data driver, wherein the current amount analyzing unit is configured to analyze and predict an output current amount according to the data signal (DATA), analyze and predict a transient current amount of the output voltage according to the output current amount, and deliver the analyzed and predicted transient current amount of the output voltage to the variation amount determining unit; wherein the variation amount determining unit is configured to determine a variation amount of the output voltage according to the transient current amount and deliver the determined variation amount of the output voltage to the output voltage varying unit; wherein the output voltage varying unit is configured to, on the basis of the data signal (DATA) and the timing signal (Sync, DDC) and the variation amount of the output voltage, determine a transient current generation section which denotes a time during which the transient current will occur, and to vary the output voltage (Vout) by the determined variation amount of the output voltage before the transient current generation section. a display panel configured to display an image; a driver including a data driver for driving the display panel; a power supply unit configured to supply an output voltage (Vout); and a timing controller configured to control the driver, wherein the power supply unit is configured to vary the output voltage (Vout) corresponding to a variation of a load for compensating a voltage variation caused by the variation of the load, before the load is changed; characterised in that the power supply unit 180 comprises a current amount analyzing unit, a variation amount determining unit, and an output voltage varying unit, and is configured to receive a data signal (DATA) from the timing controller or the data driver, and is configured to receive a timing signal (Sync, DDC) from the timing controller or the data driver, wherein the current amount analyzing unit is configured to analyze and predict an output current amount according to the data signal (DATA), analyze and predict a transient current amount of the output voltage according to the output current amount, and deliver the analyzed and predicted transient current amount of the output voltage to the variation amount determining unit; wherein the variation amount determining unit is configured to determine a variation amount of the output voltage according to the transient current amount and deliver the determined variation amount of the output voltage to the output voltage varying unit; wherein the output voltage varying unit is configured to, on the basis of the data signal (DATA) and the timing signal (Sync, DDC) and the variation amount of the output voltage, determine a transient current generation section which denotes a time during which the transient current will occur, and to vary the output voltage (Vout) by the determined variation amount of the output voltage before the transient current generation section.