A main controller of an HUD is configured to: acquire road surface information of a front road surface based on a plurality of measurement points on the front road surface, which is detected by a road surface detection sensor mounted on a vehicle with the HUD and is positioned forward of a traveling direction of the vehicle; calculate, by using the road surface information, a virtual image plane position on a virtual image plane where a virtual image of a display object is displayed, which is a display position of the virtual image for displaying the virtual image along the front road surface; and calculate a display position of a display surface within an image display device, which corresponds to the virtual image plane position, so as to output, to the image display device, a control signal for displaying the display object on the display position of the display surface.