At least one exemplary embodiment is directed to a zoom lens system having a telephoto-type configuration at the telephoto end. When assuming that an Abbe number is vd, and a partial dispersion ratio is .theta.gF, this zoom lens system includes a refractive optical element having positive refracting power made up of a solid material that can satisfy the following conditions: -2.100.times.10.sup.-3vd+0.693<.theta.gF 0.555<.theta.gF<0.9Thus, facilitating the configuration of a zoom lens system capable of appropriately correcting and/or reducing various aberrations, including a chromatic aberration straddling the entire zoom area.