PURPOSE: To form a mask with a simpler and quicker process by irradiating light to a photodecomposable resin layer to decompose said resin thereby separating a flat plate and a mask film body in the stage of transferring the mask film body on the flat plate onto a holding body.

CONSTITUTION: Chlorinated p-diazo diethyl aniline zinc chloride is dissolved in an epoxy resin soln. and the soln. is coated by spin-coating on a quartz flat plate 1 to provide a photodecomposable resin layer 2. A polyimide film 3 as an X-ray transmission layer, a gold pattern 4 as an X-ray absorption layer and a polyimide film 5 as an X-ray transmission layer for protection are successively laminated on the layer 2 to manufacture a mask film body 6. A toric holding body 7 coated with an adhesive agent on surface is adhered onto the film 5 and is cured. After the projecting part is removed, UV light is irradiated to a vertical direction 8 from the plate 1 side to decompose the resin 2. The resin layer is stripped by a thin blade.