1. A camera body to which a lens barrel having an optical system can be attached, the camera body comprising: a controller that controls the camera body; an image sensor that captures an object image; an image sensor actuator that drives the image sensor along an optical axis; and a mount to which the lens barrel is detachably mounted, the lens barrel including a plurality of lenses and a manual input device for performing focus adjustment by moving the plurality of lenses, wherein when the camera body is not capable of communicating electrically with the lens barrel, the controller, after performing a first focus adjustment by moving the image sensor along the optical axis, (i) determines manual operation of the manual input device of the lens barrel by determining a change in an optical state of the object image captured by the image sensor, (ii) in response to the determination, drives the image sensor actuator to move the image sensor to a reference position located within a movable range of the image sensor, and (iii) performs a second focus adjustment by moving the image sensor along the optical axis, and wherein the reference position is a predetermined position.