text: As a projection display device in the related art, there is known a projection display device including a light source that emits a laser light for displaying a projection, a drive reflection unit that reflects the laser light emitted from the light source and performs scanning with the laser light, a light diffusion unit including a predetermined region in which the laser light used in the scanning by the drive reflection unit is diffused, and a detection unit that detects detachment of the light diffusion unit (for example, refer to Patent Literature 1).