A terminal device with a display function enables only an operation of a desired operation key valid, and easily perform the invalidation operation. In response to switching to a predetermined function mode by manipulating a jog dial, an image in the switched function mode is displayed in a display surface, based on an image signal from a display control section. A bar is located on a borderline between a contents area and an operation area in an initial state of displaying an image. When the jog dial is manipulated by the user to thereby move the bar from the borderline to a predetermined position within the operation area, a CPU determines that the position of the bar has been moved. Then, the CPU detects a new position of the bar, and makes an operation with respect to the operation key located between the bar and the borderline invalid.