A projection display device includes: a light source that emits a first and a second laser lights; a scanning drive mirror that reflects the first and the second laser lights, and uses the first and the second laser lights in scanning; a light diffusion unit that includes a predetermined region that allows the first laser light to be transmitted therethrough, and diffuses the first laser light; a light detection unit that detects the second laser light that passed the predetermined region; and a control unit that executes a process to detect the second laser light, and determines a state of the predetermined region on the basis of a detection value of the light detection unit. In a case where the control unit determines that a defect occurs in the predetermined region as the state, the control unit executes a process to stop displaying the projection.