PURPOSE: To prevent warpage on a diffusion surface from occurring by the deformation of a screen so as to obtain a projection type display device by which a video formed on a diffusion board can be observed well by holding an optical function board or plurally superposed optical function boards at both sides by means of a pair of glass boards with pressing force by which the optical function board can be freely elongated and contracted.

CONSTITUTION: The screen is constituted by holding the diffusion board 2 at both sides by the pair of glass boards 1A and 1A with the pressing force by which it can be freely elongated and contracted. Consequently, since the board 2 can be freely elongated and contracted even though the elongation and the contraction are caused on the board 2 by temperature change, etc., the warpage on the diffusion surface is prevented from occurring. The glass board 1A itself is hardly deformed by the temperature change, etc., in comparison with the case of an acrylic board, etc., so that a problem is not generated, even though the glass board IA is fixed. Furthermore, static electricity is hardly generated on the glass board 1A in comparison with the case of the acrylic board, so that dirt is also hardly stuck on the glass board 1A.