It is an object of this invention to independently control the F-number and the number of light attenuation steps of a multi-density ND filter by using a light amount control apparatus using an iris stop and the ND filter. The iris stop mechanism made up of a plurality of aperture blades and the ND filter having a multi-density pattern are stacked in a single unit. This simultaneously realizes continuous control of the F-number, multi-step control of the light attenuation ratio of the ND filter, a substantially circular stop aperture, and a uniform transmittance distribution in the stop aperture. In the first embodiment, the driving region of an actuator is divided into an ND control region and aperture control region. This makes it possible to independently control the F-number and the number of ND steps by the single actuator.