An on-vehicle display device includes: an image display unit 6; wiring boards 8, 9 mounting a control circuit for controlling the image display unit 6; a magnesium alloy case 7 of which front recess receives the image display unit 6, and of which rear recess receives the wiring boards 8, 9; and a shield member 10 attached to the magnesium alloy case 7 for covering the rear recess. The magnesium alloy case 7 is thermally coupled to the image display unit 6 and works as a heat radiating device. The magnesium alloy case 7 is electrically coupled to the shield member 10 and works as an electromagnetic shield device together with the shield member 10.