A display device comprising: a display panel to display a frame having a resolution up to a first frame rate; a plurality of image processing units; and a processor. The processor configured to, based on change from a first mode of displaying a content, among a plurality of modes of the display device, to a second mode of displaying plural contents, change frame rates of a plurality of contents output from the plurality of image processing units to a same frame rate, mix the plurality of contents with the frame rates changed to the same frame rate, and change a vertical resolution of the mixed content. The display panel is enabled to output the mixed content, at a second frame rate greater than the first frame rate.