To obtain an optical filter using a resin material whose cost is lower than that of polyimide, whose transmittance in the visible light range is higher than that of polyimide, whose glass transition temperature is higher than that of norbornane-based resin material, whose flexural modulus is high and whose amount of outgases is scarce as a base material.

An aromatic polyamide resin material or a material including an aromatic polyamide resin material is used as a transparent synthetic resin sheet for a base material 21. The aromatic polyamide resin material is extremely small in the rate of thermal shrinkage and it has a light transmittance 90%, which is suitable for the use of an optical filter. Generally, an aromatic polyamide resin has a glass transition temperature higher than 150C, so it is higher than the glass transition temperature of a transparent composite resin sheet of PET, PEN, a norbornane-based resin and so on, and it is capable of effectively preventing the generation of wrinkles on the sheet surface. Also, as for the sheet intensity, its flexural modulus is about 10 GPa; thereby, a tough optical filter which is strong against breakage can be obtained.