A HUD including a projection display unit, a housing, a cover, a region detecting unit, and a display control unit is provided. The projection display unit includes a light modulating unit spatially modulating light emitted from a light source based on input image information and projects modulated image light onto a windshield of an automobile to display an image. The housing accommodates the projection display unit and has an opening portion through which the modulated image light exits. The cover covers the opening portion. The region detecting unit detects an object adhesion region in which an object is adhered to the cover. The display control unit controls the image information to be input to the light modulating unit to control the image to be displayed by the projection display unit. The display control unit causes the projection display unit to display an outline of the object adhesion region.