Zoom lens system, lens barrel, imaging device and camera

A zoom lens system comprising:

• at least three lens units each composed of at least one lens element, wherein
• an interval between at least any two lens units among the lens units is changed so that an optical image of an object is formed with a continuously variable magnification,
• the zoom lens system, in order from the object side to the image side, comprises:
• a first lens unit having positive optical power;
• a second lens unit that includes a lens element having a reflecting surface for bending a light beam from an object and that has negative optical power;
• and subsequent lens units including at least one lens unit having positive optical power, and
• the following condition (1) is satisfied:
• 1.50<M1/fW<3.00 (1)
• (where, Z=fT/fW>3.90)
• in which,
• M1 is an amount of optical axial movement of the first lens unit at the time of zooming from a wide-angle limit to a telephoto limit,
• fW is a focal length of the entire zoom lens system at a wide-angle limit, and
• fT is a focal length of the entire zoom lens system at a telephoto limit.