A zoom lens system comprising a first lens unit having positive optical power, a second lens unit having negative optical power, a third lens unit having positive optical power, a fourth lens unit having negative optical power, and a fifth lens unit having positive optical power, wherein the third lens unit includes at least one lens element having positive optical power and at least one lens element having negative optical power, at least the first to third lens units are moved along an optical axis in zooming so that air spaces between the respective lens units vary, thereby performing magnification change, a lens unit positioned on the image side relative to an aperture diaphragm is moved along the optical axis in focusing, and the conditions: 4.0<D / Ir<5.3 and Z=fT / fW≧9.0 (D: a total of optical axial thicknesses of respective lens units, Ir=fT×tan (ωT), ωT: a half view angle at a telephoto limit, fT and fW: focal lengths of the entire system at a telephoto limit and at a wide-angle limit) are satisfied; an imaging device; and a camera are provided.