A compact zoom lens system comprises from the object side: a first lens component of a positive refractive power; a second lens component of a negative refractive power with a variable air space between the first and second lens components; and a third lens component of a positive refractive power with a variable air space between the second and third lens components. A plurality of aspherical surfaces are employed for the realization of a compact and low-cost zoom lens system. Furthermore, a focusing operation is carried out by both of the first and second lens components or third lens component.