A first lens group (G1) fixed with respect to the image plane includes a
lens (11) having a negative refractive power, a lens (12) having a
positive refractive power and a lens (13) having a positive refractive
power. A second lens group (G2) has a negative refractive power as a
whole, and causes a zooming action when moved along the optical axis. An
aperture stop is fixed with respect to the image plane. A third lens
group (G3) includes a lens (31) having a negative refractive power and a
lens (32) having a positive refractive power, has a positive or negative
refractive power as a whole, and is fixed with respect to the direction
of the optical axis when zooming and when focusing. A fourth lens group
(G4) has a positive refractive power as a whole, and moves along the
optical axis such that the image plane, which is displaced by a movement
of the second lens group (G2) along the optical axis and by a movement of
the object, is maintained at a constant position with respect to a
reference plane. Thus, it is possible to realize a compact and high-image
quality small zoom lens that is suitable for three-CCDs.