The present invention provides a compact, high-performance, and easy-to-manufacture taking optical system that offers an extremely high zoom ratio. The taking optical system includes, from the subject side, a first lens group having a positive optical power, a second lens group having a negative optical power, a third lens group having a positive optical power, and a fourth lens group having a positive optical power. The taking optical system achieves zooming by the movements of the first to fourth lens groups and focusing by the movement of the fourth lens group. The taking optical system fulfills the following conditions: 0.05≦f3/f4≦0.95 and 7.0≦f1/fw≦20.0, where f1, f3, and f4 represent the focal lengths of the first, third, and fourth lens groups, respectively, and fw represents the focal length of the entire taking optical system at the wide-angle end thereof.