A projection apparatus comprising: an optical device configured to diffuse incident coherent light beams and change an incident direction of the coherent light beams to each position of an illumination zone with time, wherein the optical device is a hologram recording medium; an irradiation unit configured to irradiate the coherent light beams to the optical device while changing a propagation direction of the coherent light beams by continuously changing angles of the coherent light beams with time so that the coherent light beams scan the optical device, wherein the irradiation unit comprises a light source configured to emit coherent light beams and a scanning device, a light modulator, provided at the position of the illumination zone, that is illuminated by coherent light beams incident on and diffused at respective points of the optical device from the irradiation unit; a projection optical system configured to project a modulated image generated by the light modulator onto a scattering plane; a scanning device configured to change a propagation direction of the coherent light beams emitted from the light source to make the coherent light beams scan the optical device, wherein the scanning device is configured to make the coherent light beams incident on specific positions on the hologram recording medium at an incidence angle that meets the Bragg condition on the respective positions and the coherent light beams incident on the specific positions reproduce images of a scattering plate used for producing the hologram recording medium; and an intermediate optical system provided between the optical device and the light modulator, configured to restrict a diffusion angle of coherent light beams diffused by the optical device, wherein, after the diffusion angle is restricted by the intermediate optical system, the coherent light beams incident on specific positions of the hologram recording medium are diffused by the optical device, and are superimposed on one another to illuminate an entire region of the illumination zone by diffraction caused by interference fringes recorded in the hologram recording medium. an optical device configured to diffuse incident coherent light beams and change an incident direction of the coherent light beams to each position of an illumination zone with time, wherein the optical device is a hologram recording medium; an irradiation unit configured to irradiate the coherent light beams to the optical device while changing a propagation direction of the coherent light beams by continuously changing angles of the coherent light beams with time so that the coherent light beams scan the optical device, wherein the irradiation unit comprises a light source configured to emit coherent light beams and a scanning device, a light modulator, provided at the position of the illumination zone, that is illuminated by coherent light beams incident on and diffused at respective points of the optical device from the irradiation unit; a projection optical system configured to project a modulated image generated by the light modulator onto a scattering plane; a scanning device configured to change a propagation direction of the coherent light beams emitted from the light source to make the coherent light beams scan the optical device, wherein the scanning device is configured to make the coherent light beams incident on specific positions on the hologram recording medium at an incidence angle that meets the Bragg condition on the respective positions and the coherent light beams incident on the specific positions reproduce images of a scattering plate used for producing the hologram recording medium; and an intermediate optical system provided between the optical device and the light modulator, configured to restrict a diffusion angle of coherent light beams diffused by the optical device, wherein, after the diffusion angle is restricted by the intermediate optical system, the coherent light beams incident on specific positions of the hologram recording medium are diffused by the optical device, and are superimposed on one another to illuminate an entire region of the illumination zone by diffraction caused by interference fringes recorded in the hologram recording medium.