A zoom lens system comprising: sequentially from an object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a rear lens group having a positive refractive power, wherein distances among the respective lens groups adjacent to one another change during zooming from a short focal-length end to a long focal-length end, wherein the third lens group constitutes a focus lens group configured to move during focusing and includes two lenses of a negative lens and a positive lens, wherein the rear lens group includes an aperture stop SP and an N-th lens group having a negative refractive power and configured such that distances between the N-th lens group and the respective lens groups adjacent to the N-th lens group change during zooming from the short focal-length end to the long focal-length end, and wherein the zoom lens system satisfies Conditional Expression as follows: − 20 < Twt / Twm < 1, where Twt is a moving amount of the second lens group during zooming from the short focal-length end to the long focal-length end, a moving amount to the object side being indicated by a positive sign, a moving amount to an image side being indicated by a negative sign, and Twm is a moving amount of the second lens group during zooming from the short focal-length end to an intermediate focal length, a moving amount to the object side being indicated by a positive sign, a moving amount to the image side being indicated by a negative sign, the intermediate focal length being expressed by fm = (fw·ft) 1/2, where fw is a focal length of a whole system at the short focal-length end, and ft is a focal length of the whole system at the long focal-length end. sequentially from an object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a rear lens group having a positive refractive power, wherein distances among the respective lens groups adjacent to one another change during zooming from a short focal-length end to a long focal-length end, wherein the third lens group constitutes a focus lens group configured to move during focusing and includes two lenses of a negative lens and a positive lens, wherein the rear lens group includes an aperture stop SP and an N-th lens group having a negative refractive power and configured such that distances between the N-th lens group and the respective lens groups adjacent to the N-th lens group change during zooming from the short focal-length end to the long focal-length end, and wherein the zoom lens system satisfies Conditional Expression as follows: − 20 < Twt / Twm < 1, where Twt is a moving amount of the second lens group during zooming from the short focal-length end to the long focal-length end, a moving amount to the object side being indicated by a positive sign, a moving amount to an image side being indicated by a negative sign, and Twm is a moving amount of the second lens group during zooming from the short focal-length end to an intermediate focal length, a moving amount to the object side being indicated by a positive sign, a moving amount to the image side being indicated by a negative sign, the intermediate focal length being expressed by fm = (fw·ft) 1/2, where fw is a focal length of a whole system at the short focal-length end, and ft is a focal length of the whole system at the long focal-length end. Twt is a moving amount of the second lens group during zooming from the short focal-length end to the long focal-length end, a moving amount to the object side being indicated by a positive sign, a moving amount to an image side being indicated by a negative sign, and Twm is a moving amount of the second lens group during zooming from the short focal-length end to an intermediate focal length, a moving amount to the object side being indicated by a positive sign, a moving amount to the image side being indicated by a negative sign, the intermediate focal length being expressed by fm = (fw·ft) 1/2, where fw is a focal length of a whole system at the short focal-length end, and ft is a focal length of the whole system at the long focal-length end.