Zoom lens system and image taking apparatus including the same

A zoom lens system, comprising, in order from an object side to an image 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
• a fourth lens unit having a positive refractive power,
• the second lens unit and the fourth lens unit move on an optical axis during zooming, wherein:
• the third lens unit comprises, in order from the object side to the image side:
• a third A lens unit having a negative refractive power;
• and
• a third B lens unit having a positive refractive power which moves in a direction having a component in a direction perpendicular to the optical axis for moving an imaging position;
• the third B lens unit comprises at least one positive lens, and a negative lens, and comprises an aperture stop on the object side of the third A lens unit;
• and
• when an aperture diameter of the aperture stop at an open F-number at a wide angle end is Spa, a total thickness of the positive lenses configuring the third B lens unit is Dp, and a total of lens thicknesses at a height from the optical axis of a half of the aperture diameter of the aperture stop at the open F-number of the negative lens that configures the third B lens unit at the wide angle end is Kn, the following condition is satisfied
• 0.4<(Dp+Kn)/Spa<0.7.