An optical apparatus which is capable of preventing degradation of image quality caused by an ND filter. The optical apparatus incorporates an aperture stop having an aperture variable in size, and an ND filter movable with respect to the aperture of the aperture stop, an actuator that drives the ND filter, and a controller that controls the actuator. The ND filter includes a part having a size that can fully cover a first aperture that is the aperture with the aperture stop being narrowed. The controller controls the actuator so that the ND filter is moved without a halt between a first position where the part is retracted with respect to the first aperture with the aperture stop being narrowed, and a second position where the part fully covers the first aperture in any stop operation.