Image pickup apparatus having lens barrel

A lens barrel comprising:

• a first optical unit and a plurality of second optical units, and the lens barrel being configured to move each of the first optical unit and the plurality of second optical units in an optical axis direction for zooming;
• a linear movement cylinder configured to move in an optical axis direction, the linear movement cylinder including a key configured to guide the first optical unit and a plurality of linear movement grooves that extend in the optical axis direction;
• a rotation cylinder that includes an outer circumferential cam on an outer circumferential surface and a plurality of inner circumferential cams on an inner circumferential surface, the rotation cylinder being configured to move in the optical axis direction with the linear movement cylinder, the rotation cylinder being further configured to rotate around an optical axis so as to move the first optical unit in the optical axis direction through the outer circumferential cam and so as to move the second optical unit in the optical axis direction through the inner circumferential cam;
• and
• a guide bar held by the linear movement cylinder and configured to guide the plurality of second optical units in the optical axis direction,
• wherein each of the plurality of second optical units has a cam follower, and each cam follower perforates one of the plurality of linear movement grooves formed on the linear movement cylinder and engages with one of the plurality of inner circumferential cams formed on the rotation cylinder.