Zoom lens system, interchangeable lens, and imaging apparatus

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,
• wherein the rear lens group includes 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 (1) as follows:
• −20<Twt/Twm<1, (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.