The invention is directed to a lens barrel and a compact lens system incorporating the lens barrel where notches defined in a cam barrel to serve as bolt holes and disengage the studs are reduced in dimensions both along and around the optical axis, thereby ensuring enlarged cam formation ranges in the cam barrel and resultantly downsizing the lens system as a whole. The lens system of the present invention comprises a foremost group of lens elements closest to the object, a rearmost group of lens elements farthest from the object, a first fixed barrel, a linearly-shuttling barrel residing inside the first fixed barrel so as to be slidable along the optical axis, for carrying the rearmost group of lens elements, a cam barrel having at least two types of cams and residing outside the first fixed barrel so as to be rotatable about the optical axis, a second fixed barrel residing outside the cam barrel, linearly-sliding studs positioned in a forward edge of the linearly-shuttling barrel closer to the object, and a lens barrel residing over an inner surface of the second fixed barrel so as to be slidable thereover and provided with linear grooves in which the linearly-sliding studs fitted, for carrying the foremost group of lens elements.