A manually adjustable apparatus for a zoom lens includes a body, a lens set, a sliding base, a rack sliding base, and a transmission gear. The lens set is installed at the body. There is an outer gear located at the rear end of the lens cone of the lens set. The sliding base is fastened at the body. On the bottom surface of the rack sliding base, there is a rack. The transmission gear is pivoted on the body and is interlocked with the rack and the outer gear. The present invention turns the rack sliding base manually to make the lens cone rotate and move via the rack, the transmission gear, and the outer gear for controlling and zooming the lens set. No power is needed so that the power loading of the still camera is reduced, and the cost of the still camera is reduced.