A variable magnification optical system consists of a positive first lens-group, a negative second lens-group, a positive third lens-group and a positive fourth lens-group in this order from an object side. The first lens-group and the third lens-group are fixed when magnification is changed from a wide-angle end to a telephoto end, and the magnification is changed from the wide-angle end to the telephoto end by moving the second lens-group toward an image side, and correction of an image plane and focusing, which have been necessitated by magnification change, are performed by moving the fourth lens-group. The first lens-group consists of two positive lenses and a negative lens in this order from the object side. The second lens-group consists of a negative 21st lens, a positive 22nd lens, a negative 23rd lens and a negative 24th lens in this order from the object side.