An optical diaphragm device includes a plurality of diaphragm blades including a first fixing boss protruding from one surface of a first planar plate toward a side in a first direction; and a moving boss protruding from another surface of the first planar plate toward a side in a second direction. The optical diagram device includes a plurality of light leakage prevention blades including a second fixing boss protruding from one surface of a second planar plate toward the side in the first direction. The optical diagram device includes a drive ring including a plurality of first cam grooves; a housing body capable of accommodating the diaphragm blades, the light leakage prevention blades, and the drive ring. A second cam groove is in the light leakage prevention blade. The moving boss is in the second cam groove, and is in the first cam groove.