A projection display device includes: a light modulation unit that spatially modulates, in accordance with image data that has been input, light emitted by a light source; a projection optical system that projects the light that has been spatially modulated onto a projection surface of a vehicle; a measurement information acquisition unit that acquires measurement information measured by an information measuring device; an image display control unit that performs either first display control or second display control as defined herein; and a warning determination unit that determines, in accordance with the measurement information, whether or not a warning is necessary, and the image display control unit performs the second display control when the warning determination unit determines that the warning is necessary, and performs the first display control when the warning determination unit determines that the warning is not necessary.