A light quantity control device includes: a bottom board having an opening; a first blade and a second blade linearly moving in opposing directions and changing in an opening area of the opening; a supporting blade overlapping the first blade and closing the opening in cooperation with the first blade and the second blade; and a driving lever connected to the first blade, the second blade, and the supporting blade, and driving the first blade, the second blade, and the supporting blade by rotation of the driving lever. The first blade and the supporting blade are engaged with an identical pin provided in the driving lever. The first blade and the supporting blade are misaligned in such a way to reduce an overlapping degree of the first blade and the supporting blade. The first blade and the supporting blade bring the opening to the fully closed state in cooperation with the second blade.