Provided is a display device of a mobile phone with a sub memory. The display device includes a display panel for displaying application data and state display data corresponding to a main image data signal used to display various application data and a sub image data signal including state display data and picture control signals, a sub memory for storing state display data and picture control signals for outputting state display data and picture control signals to the display panel, and a display driver which drives images or data to be displayed on the display panel.