DIAPHRAGM DEVICE

PROBLEM TO BE SOLVED: To provide a diaphragm device whose diaphragm opening is shaped like a true circle within one stage diaphragm under the control of the minimum f value due to diaphragm to be used for a zoom lens by reducing the number of aperture blades as far as possible. SOLUTION: Aperture blades are formed so that more than three aperture blades can be prevented from being overlapped even in the minimum diaphragm state, and an inner edge part 5 related with the formation of the aperture diaphragm is constituted of a root inner edge part 5a close to the turning center, a top end inner edge part 5b far from the turning center, and an intermediate inner edge part 5c between the root inner edge and the top end inner edge, and the root inner edge part is formed so that the aperture diaphragm can be shaped like a pseudo circle between the open state and the state a little stopped from the open state, and connected via a circular- arc shape whose center is positioned outside the inner edge part to the intermediate inner part, and the top end inner edge part is formed like a circular-arc whose center is positioned outside the inner edge part, and the intermediate inner edge part is formed so that the opening shape of the aperture diaphragm in the state a little stopped from the open state can be shaped like a true circle by the intermediate inner edge part.