A zoom optical system has, in order from the object side, a first lens unit with negative refracting power, including one biconcave-shaped lens component, a second lens unit with positive refracting power, a third lens unit with negative refracting power, and a fourth lens unit with positive refracting power. When the magnification of the zoom optical system is changed, relative distances between individual lens units are varied and the zoom optical system satisfies the following condition: 0.2≦dCD/fw≦1.2 where dCD is spacing between the third lens unit and the fourth lens unit on the optical axis in infinite focusing at a wide-angle position and fw is the focal length of the entire system of the zoom optical system at the wide-angle position.