An aperture stop apparatus configured to control a light amount in each of two optical systems arranged in parallel includes a drive gear, a single driving source configured to drive the drive gear, a base member, two aperture stops as iris stops each having three or more blade members, and two rotating members each including a gear portion engaged with the drive gear. Each aperture stop is operated as a corresponding one of the rotating members rotates. A rotation of a drive gear driven by the driving source is transmitted to the two rotating members through the gear portions provided to the rotating members and engaged with the drive gear.