A display device, includes: a main display panel; a main driving unit which comprises a driving voltage generating unit that generates a plurality of driving voltages to be supplied for the main display panel and a first driving voltage terminal that outputs the driving voltages, and drives the main display panel; a sub-display panel; a sub-driving unit which comprises a source power terminal that receives source power from the main driving unit, a second driving voltage generating unit, a second driving voltage terminal that is connected with first driving voltage terminal and a switching unit that switches the source power supplied from the source power terminal to the second driving voltage generating unit, and drives the sub-display panel; and a controller which controls the switching unit not to supply the source power from the source power terminal to the second driving voltage generating unit if the main display panel is in a standby mode in which an image is not displayed on the main display panel.