PURPOSE: To facilitate a change of light source of a luminous display means by providing the first hologram of reflecting display light diffracted from the luminous display means and the second hologram of reflecting the display light, here diffraction reflected, again diffracted to project a display image in a visual field of a viewer.
CONSTITUTION: In the case of applying a device to a head up display of a vehicle, this hologram display device 10 is constituted of a display device 11 for radiating a display light beam of speed or the like, first hologram 21 set up in the interior side of a dash board 41 and the second hologram 22 buried in a front glass 42. Each hologram 21, 22, in the case of assuming α1, α2 for respective incident angle, β1, β2 for outgoing angle and θ for mounting angle formed by normals of both the holograms 21, 22, is arranged so as to satisfy an expression of {cos(β1+θ)/cosβ1}.{(sinα1-sinβ1)/(sinα2-sinβ2)}=-1. In this way, the display device 11 can be arranged in the dash board 41, to facilitate a change or the like of the display device.
KOIKE OSAMU
NANBA SHINJI
