A projection type image display apparatus that carries out image display by projecting light onto a screen, comprising: a spatial light modulator that modulates incident light according to an incidence position based on an image as a display object, and emits the light; an illumination unit that supplies illumination light to the spatial light modulator; and a projection optical system that guides illumination light modulated by the spatial light modulator to the screen, and projects the image onto the screen, wherein the illumination unit includes: a hologram recording medium on which an image of a scatter plate is recorded as a hologram by using reference light (Lref) composed of a parallel light flux, a coherent light source that generates a coherent light beam with a wavelength capable of reproducing the image of the scatter plate, and a light beam scanning device that irradiates the light beam onto the hologram recording medium, and scans the light beam by irradiating the light beam onto the hologram recording medium in a direction parallel to the reference light (Lref) and changes an irradiation position of the light beam on the hologram recording medium with time while moving the light beam parallel, the light beam scanning device including a movable reflecting mirror and a drive mechanism that drives by sliding the movable reflecting mirror, and the spatial light modulator is disposed at a production position of the reproduction image of the scatter plate obtained from the hologram recording medium. a spatial light modulator that modulates incident light according to an incidence position based on an image as a display object, and emits the light; an illumination unit that supplies illumination light to the spatial light modulator; and a projection optical system that guides illumination light modulated by the spatial light modulator to the screen, and projects the image onto the screen, wherein the illumination unit includes: a hologram recording medium on which an image of a scatter plate is recorded as a hologram by using reference light (Lref) composed of a parallel light flux, a coherent light source that generates a coherent light beam with a wavelength capable of reproducing the image of the scatter plate, and a light beam scanning device that irradiates the light beam onto the hologram recording medium, and scans the light beam by irradiating the light beam onto the hologram recording medium in a direction parallel to the reference light (Lref) and changes an irradiation position of the light beam on the hologram recording medium with time while moving the light beam parallel, the light beam scanning device including a movable reflecting mirror and a drive mechanism that drives by sliding the movable reflecting mirror, and the spatial light modulator is disposed at a production position of the reproduction image of the scatter plate obtained from the hologram recording medium. a hologram recording medium on which an image of a scatter plate is recorded as a hologram by using reference light (Lref) composed of a parallel light flux, a coherent light source that generates a coherent light beam with a wavelength capable of reproducing the image of the scatter plate, and a light beam scanning device that irradiates the light beam onto the hologram recording medium, and scans the light beam by irradiating the light beam onto the hologram recording medium in a direction parallel to the reference light (Lref) and changes an irradiation position of the light beam on the hologram recording medium with time while moving the light beam parallel, the light beam scanning device including a movable reflecting mirror and a drive mechanism that drives by sliding the movable reflecting mirror, and the spatial light modulator is disposed at a production position of the reproduction image of the scatter plate obtained from the hologram recording medium.