A zoom lens system having an image shake correcting capability has, from the object side to the image side: a first lens group having a positive optical power, a second lens group having a negative optical power, a third lens group having a positive optical power, a fourth lens group having a negative optical power, and a fifth lens group having a positive optical power. The third lens group includes a positive lens component and a cemented lens element having a positive optical power. The cemented lens element is moved in a direction perpendicular to the optical axis to correct image shake, and the conditional formula 1.7