A projection display device for use in any one of a vehicle-mounted type display, a helmet-embedded type display, and an eyeglass type display, comprising: a light source arranged to emit a first laser light for displaying a projection and a second laser light for inspection; a drive reflection unit arranged to reflect the first laser light and the second laser light emitted from the light source, and to use the first laser light and the second laser light in scanning; a light diffusion unit that includes a predetermined region arranged to allow the first laser light used in the scanning by the drive reflection unit to be transmitted through the predetermined region, and to diffuse the first laser light; a light detection unit arranged to detect the second laser light that reflects - a state of an incident surface of the light diffusion unit in the predetermined region, or - a state of an incident surface and an emission surface of the light diffusion unit in the predetermined region, and an internal state of the light diffusion unit in the predetermined region; and a control unit arranged to execute a process to detect the second laser light, and to determine a state of the predetermined region of the light diffusion unit on the basis of a detection value of the light detection unit, wherein the light diffusion unit is a microlens array, and the control unit is arranged such that in a case where the control unit determines that a defect occurs in the predetermined region of the light diffusion unit as the state of the predetermined region of the light diffusion unit, the control unit executes a process to stop displaying the projection. a light source arranged to emit a first laser light for displaying a projection and a second laser light for inspection; a drive reflection unit arranged to reflect the first laser light and the second laser light emitted from the light source, and to use the first laser light and the second laser light in scanning; a light diffusion unit that includes a predetermined region arranged to allow the first laser light used in the scanning by the drive reflection unit to be transmitted through the predetermined region, and to diffuse the first laser light; a light detection unit arranged to detect the second laser light that reflects - a state of an incident surface of the light diffusion unit in the predetermined region, or - a state of an incident surface and an emission surface of the light diffusion unit in the predetermined region, and an internal state of the light diffusion unit in the predetermined region; and - a state of an incident surface of the light diffusion unit in the predetermined region, or - a state of an incident surface and an emission surface of the light diffusion unit in the predetermined region, and an internal state of the light diffusion unit in the predetermined region; and a control unit arranged to execute a process to detect the second laser light, and to determine a state of the predetermined region of the light diffusion unit on the basis of a detection value of the light detection unit, wherein the light diffusion unit is a microlens array, and the control unit is arranged such that in a case where the control unit determines that a defect occurs in the predetermined region of the light diffusion unit as the state of the predetermined region of the light diffusion unit, the control unit executes a process to stop displaying the projection.