1. A user interface device operable to perform a display function of displaying an image on a display screen, and a touch panel function of outputting successive locations of the user's finger touch point on a touch screen over time, comprising: a screen-pad controller configured to display a reference image on the display screen to form a screen pad, such that the reference image is a reduced duplicate of an original image being displayed on the display screen; a touch determining unit configured to determine whether or not the finger has been touched to the screen pad; a pointer displaying unit configured to be operable in response to the touch determining unit determining that the finger has been touched to the screen pad, to display a pointer on the original image being displayed on the display screen, to indicate a location on the display screen, which corresponds to a position at which the user has touched the finger to the screen pad; and an operation controller configured to invoke an operation associated with the location that the pointer is indicating.