PURPOSE: To perform set operation with weak force by operating a part located on the other side of the aperture of one blade in a group of blades by arranging a set mechanism which moves the group of blades from the stationary position to the tensing position in the other side of the aperture.

CONSTITUTION: When a string 30 for setting a shutter mechanism moves in the arrow direction, as the side face 25b as a closed set plate 25 contacts with the bend 2a of a cover plate 2, both an opened set plate 20 and the closed set plate 25 start going down through the 1st crank lever 23 and the 2nd crank lever 24. Therefore, an arm 20a pushed a pin 15, and a blade 15 forming opened slit, an opened main arm 12, an opened subarm 13 and an opened driving lever 4 perform right turning oscillation or right turning movement with a shaft 5 or a shaft 14 as a fulcrum, and a closed main arm 16, a closed subarm 17 and a closed driving lever 8 perform right turning oscillation or right turning movement.