An optical apparatus includes a zoom optical system including a focusing
lens unit, a first cam member that rotates around the optical axis and
moves along the optical axis in a magnification-changing operation, the
first cam member including a focus cam portion for driving the focusing
lens unit, and a speed-changing mechanism that changes the relative
rotational speed between the focusing lens unit and the first cam member
in accordance with the focal length of the zoom optical system in the
magnification-changing operation. The speed-changing mechanism moves
along the optical axis in the magnification-changing operation. In
addition, the speed-changing mechanism includes a transmission member
that is rotatable around the optical axis with respect to the first cam
member and that includes a speed-changing cam portion for changing at
least one of the rotational speed and the rotational direction of the
focusing lens unit.