A zoom lens system (ZL) comprising, in order from an object side, a first lens group (Gr1) having a negative optical power, a second lens group (Gr2) having a positive optical power, a third lens group (Gr3) having a positive optical power, and a fourth lens group (Gr4) having a negative optical power, the zoom lens system (ZL) configured to perform magnification variation by varying an axial group-to-group distance, wherein during magnification variation from a wide angle end (W) to a telephoto end (T), a distance between the first lens group (Gr1) and the second lens group (Gr2) is configured to be reduced, a distance between the second lens group (Gr2) and the third lens group (Gr3) is configured to be reduced, and a distance between the third lens group (Gr3) and the fourth lens group (Gr4) is configured to be increased, the second lens group (Gr2) is composed of, in order from the object side, a second-a lens group (Gr2a) and a second-b lens group (Gr2b), the second-a lens group (Gr2a) having a positive optical power, and focusing to a nearby object is configured to be performed by moving the second-a lens group (Gr2a) toward an image side, characterized in that the zoom lens system comprises an aperture stop (ST) located at the most object-side position in the second-b lens group (Gr2b), and configured to move as a part of the second-b lens group (Gr2b) during magnification variation, a distance between the second-a lens group (Gr2a) and the second-b lens group (Gr2b) is configured to be varied during magnification variation, the second-b lens group (Gr2b) and the fourth lens group (Gr4) are configured to move integrally with each other during magnification variation, and conditional formulae , and below are satisfied: 0.6 < f 4 / f 1 < 5.0 − 2.0 < 1 − β 2 w 2 × β rw 2 < − 0.1 0.75 < M 4 / M 3 < 0.95 where β2w represents a paraxial lateral magnification of the second-a lens group (Gr2a) at the wide angle end (W); Prw represents a composite paraxial lateral magnification of the second-b lens group (Gr2b) and subsequent lens groups at the wide angle end (W); f1 represents a focal length of the first lens group (Gr1); f4 represents a focal length of the fourth lens group (Gr4); M4 represents an amount of movement of the fourth lens group (Gr4) on an optical axis (AX) during magnification variation from the wide angle end (W) to the telephoto end (T); and M3 represents an amount of movement of the third lens group (Gr3) on the optical axis (AX) during magnification variation from the wide angle end (W) to the telephoto end (T). β2w represents a paraxial lateral magnification of the second-a lens group (Gr2a) at the wide angle end (W); Prw represents a composite paraxial lateral magnification of the second-b lens group (Gr2b) and subsequent lens groups at the wide angle end (W); f1 represents a focal length of the first lens group (Gr1); f4 represents a focal length of the fourth lens group (Gr4); M4 represents an amount of movement of the fourth lens group (Gr4) on an optical axis (AX) during magnification variation from the wide angle end (W) to the telephoto end (T); and M3 represents an amount of movement of the third lens group (Gr3) on the optical axis (AX) during magnification variation from the wide angle end (W) to the telephoto end (T). <EOS>