The virtual images 464, 464′ in FIGS. 12D and 13D may be erased just after completing movement of the virtual vehicle or may be maintained for a short period of time in a state of being displayed at the same positions respectively on the front windshield 15 and the monitor device 24. Further, the moving images from the virtual image 461, 461′ to the virtual image 464, 464′ may be displayed repeatedly.