PROJECTION DISPLAY DEVICE, CONTROL METHOD FOR PROJECTION DISPLAY DEVICE, AND CONTROL PROGRAM FOR PROJECTION DISPLAY DEVICE

An HUD includes: a projection display unit that includes a light modulating unit spatially modulating light emitted from a light source on the basis of input image information and projects image light obtained as a result of spatial modulation onto a windshield of a automobile to display an image based on the image light; a housing that accommodates the projection display unit and has an opening portion K through which the image light exits; a cover that covers the opening portion K; a region detecting unit that detects an object adhesion region in which an object is adhered to the cover; and a display control unit that 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.