A variable power optical system (1) comprises a first lens group (11) having a negative optical power, a second lens group (12) having a positive optical power, and a third lens group (13). The first to third lens groups are arranged in order from the object side to the image side. The first lens group (11) is composed of one negative lens (111) and is fixed in variable power. The third lens group (13) includes at least one aspherical surface. When the third lens group is divided into a front group and a rear group with the largest air space in the third group, the front group has a negative optical power, and the rear group has a positive optical power.