Abstract: In a holding frame of the aperture mechanism is formed a holding portion to which is to be fitted a drive mechanism for opening and closing aperture blades. The holding portion can be fitted with either an electrical drive mechanism, having an iris meter, for electrically opening and closing aperture blades and or a manual drive mechanism for supporting rotatably an iris ring to manually open and close the aperture blades. Thus, an aperture mechanism whose manufacturing cost can be substantially reduced by enabling either or both of an electrical drive mechanism for electrically driving aperture blades and a manual drive mechanism for manually driving them to be fitted to a common holding frame of the aperture mechanism is to be provided.