To cope with a high speed operation by enabling the smooth operation of a light quantity adjustment device.

A light quantity adjustment device 6 comprises: a base member 50 with a fixed aperture 54 and a plurality of cam grooves 51; a plurality of shading vanes 10 having their respective drive pins 11 and cam pins 12 engaged with the cam grooves and arranged in a circumferential direction of the fixed aperture and forming a variable aperture through which light passes; a drive ring 20 for transferring a driving force to the drive pins by rotating in the circumferential direction of the fixed aperture with respect to a base member, thereby rotating the plurality of shading vanes; and a drive source 1 for rotating and driving the drive ring. The drive ring has fist vane support parts 122 which are portions formed so as to project radially outside from the a ring shaped part and have drive holes engaged with the drive pins, and supports vane faces of the shading vanes, opposite the base member, by use of the first vane support parts.