A variable power optical system (ZL) used for an optical apparatus, such as a camera (1), includes, in order from an object: a first lens group (G1) having positive refractive power; a second lens group (G2) having negative refractive power; a third lens group (G3) having positive refractive power; and a fourth lens group (G4) having positive refractive power. The distance between the respective lens groups changes upon zooming from the wide-angle end state to the telephoto end state. The third lens group (G3) includes: an intermediate group (G3b) constituted by a positive lens, a negative lens, a negative lens, and a positive lens; and an image side group (G3c) having negative refractive power and disposed to an image side of the intermediate group (G3b). Upon focusing, the position of the intermediate group (G3b) with respect to the image plane is fixed and the image side group (G3c) moves along the optical axis.