A display device according synthesizes icons and messages with a portion where no descriptive display image is displayed by OSD for display. Icon functions are set by a PC so that the setting of the operation of the PC and the display device, and the setting of an external device can be conducted. The number of lines of the message to be displayed is determined according to distortion correction at the case of oblique projection to correct position coordinates detected by a camera. In a presentation system including an interactive white board device, the display device (for example, a liquid crystal projector), and the PC, the display of the icons are improved to extend the functions, and the display of the messages at the case of oblique projection, and a position detection precision on a screen by the camera incorporated into the display device are improved.