Providing a zoom lens system having a high zoom ratio being compact with high optical performance. The system includes, in order from an object along an optical axis, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, at least one lens group having positive refractive power, and an n-th lens group GN being disposed to the most image side. The n-th lens group GN with positive refractive power includes, in order from the object, a front group GNa and a rear group GNb having positive refractive power. Focusing on an object is carried out by moving the rear group GNb along the optical axis, and a given conditional expression is satisfied.