In order to provide an optical apparatus capable of adjusting a light amount in each of a plurality of optical systems with a simple structure, the optical apparatus according to the present invention includes a plurality of optical systems each of which includes a stop, a storing unit configured to store information indicating a relationship between target aperture diameters of the stop and target light amounts in the respective optical systems, and a controller configured to adjust a light amount by changing an aperture diameter of the stop in the respective optical systems based on the information.