To provide a small and lightweight display device and the like which can display an image as a virtual at a position with a desired distance and never gives displeasure to a user.

The display device is provided with an LCD 115 for generating an image; an HOE 25 for displaying an image generated by this LCD 115 as a virtual VI, so that the image is superimposed over an observing object substantially directly observed by an observer; a liquid lens 257 disposed between the LCD 115 and the HOE 25; and a voltage-controlled circuit 258 for varying the lens shape by controlling a voltage to be applied to this liquid lens 257 to adjust a focal distance, and adjusting the distance between the HOE 25 to the virtual VI so that the focal distance may be the same as the distance between the HOE 25 and an observing object.