To provide a light quantity adjustment device capable of suppressing peeling of laser-welded blade members and forming an exact exposure aperture.

The light quantity adjustment device comprises: a substrate including an optical path aperture; the blade members for opening/closing the optical path aperture; a drive ring for driving the blade members; and driving means for rotating the drive ring with the optical path aperture as a center. Each of the blade members includes: a blade substrate which forms a throttle forming section for opening/closing the optical path aperture and a base end portion in which a pair of support shafts fitted to the substrate and the drive ring are disposed at a base end of the throttle forming section and does not transmit laser light; and an auxiliary substrate which includes support shafts stuck to the base end portion by laser welding and transmits laser light. In the auxiliary substrate, a groove section is formed to allow a solvent of the blade substrate dissolving by the laser to flow out to a welding region irradiated with laser on a front surface side opposed to the blade substrate.