Abstract: A zoom lens system has, in order from an object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, an aperture stop, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power; during magnification change, the first lens unit, the second lens unit, the third lens unit, the fourth lens unit and the aperture stop move; the first lens unit includes a negative lens and a positive lens in order from the object side; the second lens unit includes a negative lens and a positive lens in order from the object side; the third lens unit includes three or less lenses including one positive lens and one negative lens; and the fourth lens unit includes one positive lens.