To constitute almost a true circle shape in all range between a full aperture and a minimum aperture without increasing the number of aperture blades in an aperture device.

An inner edge part forming the aperture of the aperture blade 22 comprises a three parts, that is, a base inner edge part 22a near a pin 25, a tip inner edge part 22b apart from the pin 25, and a middle inner edge part 22c located between the parts 22a, 22b. The parts 22a, 22b comprise an arc 33 having a radius R1 of the full aperture with a center on an optical axis S1. The part 22c comprises a plurality of arcs along a plurality of circles passing an end point P of the part 22a. The radiuses of the circles comprising the part 22c are set to be gradually larger from the part 22a to the part 22b corresponding to the radius of the aperture between the full aperture and the minimum aperture. The centers of respective arcs are located on or near the circumference 40 of a circle passing the optical axis S1 and having the radius R0 with a center on the turning center of the aperture blade 22.