A zoom lens system includes, in order from an object, a front group G1 having negative refractive power, a rear group G2 having positive refractive power, zooming being conducted by varying a distance between the front group G1 and the rear group G2, the front group G1 including at least a negative lens and a positive lens, and the rear group G2 including, in order from an object side, a first partial group LA having positive refractive power, a second partial group LB having negative refractive power, a third partial group LC having positive refractive power and a negative lens LD, and predetermined conditions being satisfied, thereby providing a zoom lens system which is compact in size, and has small back focus and excellent optical property.