The objective of the present invention is to provide a zoom lens system having an f-number of approximately 1.3 at the wide extremity, a half angle-of-view of 75 degrees, and a zoom ratio of approximately 3:1. The solution to this objective is to provide a zoom lens system including a first lens group, having a negative refractive power, a diaphragm, and a second lens group, having a positive refractive power, in that order from the object side; wherein the first lens group and the second lens group move in the optical axis direction so that the distance therebetween decreases upon zooming from the wide-angle extremity to the telephoto extremity,