Zoom lens systems suitable as a projection lens system have been proposed in Patent Literatures 1 to 3, etc. For example, Patent Literature 1 describes a zoom lens system having a six-group design with a negative-negative-positive-negative-positive-positive arrangement, where first and sixth lens groups remain stationary during zooming, an aperture stop is disposed between third and fourth lens groups, and a diffractive optical element is used to correct chromatic aberrations. Patent Literature 2 describes a zoom lens system having a six-group design with a negative-negative-positive-negative-positive-positive arrangement, where first, third, and fifth lens groups remain stationary during zooming. This zoom lens system it is a projection lens system having a wide angle of view and advantageous in achieving compactness, which makes it suitable for use in portable data projectors. Patent Literature 3 describes a zoom lens system having a six-group design with a negative-positive-positive-negative-(positive or negative)-positive arrangement, where movable lens groups movable during zooming and the refractive power arrangement of each lens group are appropriately set. This is a compact zoom lens having a long backfocus, where various aberrations are satisfactorily corrected.