A light amount adjusting device includes: a board including an opening; a linear moving blade linearly and movably supported by the board; and a swinging blade swingably supported by the board, wherein: the linear moving blade and the swinging blade are receded from the opening to form a fully opened state; the linear moving blade covers the opening to form a fully closed state; and the swinging blade has a small aperture opening with a diameter smaller than a diameter of the opening, and causes the small aperture opening and the opening to be overlapped with each other to form a small aperture state.