PURPOSE: To obtain a zoom lens which is compact and corrects an aberration satisfactorily by constituting so that an optical system provided with three lens groups having positive, negative and negative powers, and the fourth lens group which is fixed in the course of zooming, in order from an object side satisfies prescribed conditions.

CONSTITUTION: A titled zoom lens consists of the first lens group G1 which is fixed in the course of zooming and has a positive power, the second and the third lens groups G2, G3 which are movably by zooming and have a negative power, and the fourth lens group G4 which is fixed in the course of zooming, in order from an object side. When executing a zooming to a telescope end from a wide angle end, the second lens group G2 moves monotonously to an image side from the object side along the optical axis, and the third lens group G3 executes a reciprocating motion on the optical axis. This optical system is constituted so as to satisfy conditions of an expression I and an expression II, and in the ex pressions, fT denotes a focal distance of a telephoto end of the whole system, FT denotes the minimum F-number at a telephoto end, f1 denotes a focal dis tance of the first lens group G1, β2w denotes a magnification in a wide angle end of the second lens group G2, and V denotes a zoom ratio, respectively.