In an on-vehicle head up display device employing a catoptric system for a windsheid glass of an automobile to project a display image onto an inner surface of the windshield glass, an optical system for letting a virtual image of the display image of a display means enter the windshield glass is adapted to make an angle formed by light beams of the virtual image entering the windshield glass less than a monocular resolving power. Further, an optical means for correcting parallax of the light beams of the virtual image is provided between the optical system and the windshield glass. Thus, a double image formation and binocular parallax may be eliminated. FIG.9