PURPOSE: To improve light shielding property and strength by employing a shutter base where the edge of an aperture when each slit forming blade traveling the surface of the shutter base is positioned so as to shield light is thicker than the edge of said aperture when said each blade overlapped is positioned so as to opened it.

CONSTITUTION: The pre-travel position of the rear blade sector means that the slit forming blade 1c and four divided blades 11d in the 2nd blade sector are all overlapped and they are positioned in a thicker part 31 including the edge part 31a on one side of the aperture 33. On the other hand, the post-travel position of said sector means that the slit forming blade 11c and four divided blades 11d in said sector spread and lie in the entire area of the aperture to shield light. Since the thicker part 29 is thicker than a thicker part 31 after the 2nd blade sector travels, the blades 11c and 11d spread and an interval between them is narrowed in their thickness direction, thereby considerably improving light shielding property.