A stepwise variable zoom lens system includes, in order from an object side, a first lens group with a negative refractive power, a second lens group with a positive refractive power, a third lens group with a negative refractive power and a fourth lens group with a positive refractive power. Each of the first lens group, the third lens group and the fourth lens group is constructed from a single block. The first lens group and the fourth lens group are fixed. The second lens group and the third lens group are moveable to be selectively positioned at the wide-angle zoom position and the telephoto zoom position for zooming. The third lens group is finely adjustable for focusing when the object is positioned in different distance.