A blade driving device includes an opening forming member, and a plurality of groups of blades that are pivotably disposed in a ring form around an opening portion of the opening forming member. The plurality of groups of blades include a first group of blades and a second group of blades, in a process of changing from a first circular light passage opening formed by the first group to a second circular light passage opening formed by the second group, the first group that is adjacent to the second group and has finished forming the first circular light passage opening remains in the opening portion, thereby acting to substantially suppressing warp, in an optical axis direction, of the second group that forms the second circular light passage opening on an inner side thereof.