1. A terminal having a plurality of display buttons for displaying a plurality of information images included in a display image, the terminal comprising: an information image provider to output each of the plurality of information images to a display image processor; the display image processor to generate the display image, the display image comprising information images to be displayed in a sub display unit which is comprised of the plurality of display buttons and an image to be displayed in a main display unit, by synthesizing the plurality of information images input from the information image provider with the image to be displayed in the main display unit, wherein the number of information images to be displayed in the sub display unit is more than the number of display buttons, and the information images which are more repeatedly selected by a user among the information images to be displayed in the sub display unit are firstly displayed on the display buttons according to the analyzed number of repeated selections of each of the information images; a display image displayer to receive the display image from the display image processor and display the display image, the display image displayer including the main display unit and the sub display unit comprised of the plurality of display buttons, the main display unit comprising a first region of the display image displayer where the main display unit displays the image to be displayed in the main display unit, the sub display unit comprising a second region of the display image displayer where the sub display unit displays the plurality of information images, the first region being larger than the second region; and a controller to control one or more operations of the information image provider, the display image processor, and the display image displayer, wherein the image to be displayed in the main display unit shows a function that the terminal is performing, and the information images show sub-functions of the function that the terminal is performing.