An optical apparatus is disclosed which can prevent displacement of subject images due to an initializing operation of the image stabilizing unit from being seen by a photographer through a finder. The apparatus comprises an image-stabilizing unit which includes a movable unit movable for image stabilization and balls movable in conjunction with the movement of the movable unit, and a controller which controls operations of the movable unit. The controller causes the movable unit to perform a specific operation for moving the balls to a specific position in response to mounting of the optical apparatus on another optical apparatus, the specific operation being a different operation from an image stabilization operation of the image-stabilizing unit.