To provide an optical filter with a less thermal deformation and is light in weight by increasing the rigidity so as to sufficiently protect a plasma display panel(PDP).

An optical filter 1 is fitted to a front of a display screen of a PDP 2. The optical filter 1 is composed of a plywood composed of an acrylic board 1a and a glass board 1b. The acrylic board 1a and the glass board 1b are stuck by a transparent gel-like adhesives 1c. The thickness of the acrylic board 1a and the glass board 1b is nearly 1mm. The optical filter 1 formed by stucking the acrylic board 1a and the glass board 1b by the transparent adhesives 1c is fitted to a display screen of a front frame 3 of the display device and fixed with a machine screw 5 by using a mount metallic fixture 4. Further, a glass board is made to be reinforced glass board 1b by chemical processing.