A coordinate measuring unit measures an x-coordinate, a y-coordinate and a z-coordinate indicating an object position according to a change in the position of an object located within a predetermined distance from a panel surface. A display control unit causes a display unit to display a first mark image defining a peripheral distance of a positon determined by the x- and y-coordinates together with predetermined images. The display control unit causes the display unit to display the first mark image such that an area defined by the first mark image becomes smaller as the z-coordinate becomes smaller.