To solve such a problem that the accuracy of exposure second tends to be unstable by repetition of contact/non-contact of light shielding blades with each other in the case of traveling of a shutter.

In the shutter constituted by a plurality of light shielding blades 2c to 2g and having a group 2 of light shielding blades for opening/closing a light passing opening 1a by superposition and a developing operation and arm members 2a, 2b for performing the superposition and the developing operation of the group of light shielding blades by supporting the group 2 of light shielding blades, at least one light shielding blades 2d, 2f of the group of light shielding blades is formed so that thickness in the vicinity of one end part on the far side from a supporting part by the arm members 2a, 2b of both end parts of the light shielding blades 2d, 2f in the longitudinal direction becomes thicker than the thickness of other parts.