PURPOSE: To obtain a high speed shutter device with high strength which is light and excellent in durability by making a prepreg sheet, which is a stock material formed of a carbon fiber and matrix resin, the base of the structural material of an arm for a shutter.

CONSTITUTION: The arms 10 and 11 for the shutter are formed of the prepreg sheet impregnating plastic resin where many carbon fibers are set as reinforcement materials. For example, the prepreg sheet 1 obtained by impregnating the matrix resin 1b to the carbon fibers 1a in long fiber shape which are arranged in one direction and forming it in a B-stage shape is used as the structural material. And it is assumed that the thickness of the prepreg sheet (including a cloth) is about 100W150μm. Thus, the arm for the shutter with high strength which is light and excellent in planeness can be obtained.