A variable magnification optical system includes a plurality of lens element, and includes in order from an object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and at least one lens unit. An aperture stop is either positioned between the second lens unit and the third lens unit, or positioned in the third lens unit. At the time of zooming from a wide angle end to a telephoto end, the first lens unit is fixed, the second lens unit moves from the object side to an image-plane side, and at least one of lens units positioned on an image side of the aperture stop moves. The first lens unit includes at least four positive lens elements and at least two negative lens elements.