A zoom lens system, in order from an object side to an image side, comprising: a first lens unit having negative optical power; a second lens unit having positive optical power; a third lens unit having negative optical power; and a fourth lens unit having positive optical power, wherein the third lens unit is composed of two or less lens elements, the fourth lens unit is composed of two or less lens elements, the first lens unit has at least one air space between lens elements constituting the first lens unit, and the condition: Dair/fW>0.75 (Dair: an air space located on the most object side in the first lens unit, fW: a focal length of the entire system at a wide-angle limit) is satisfied; an imaging device; and a camera are provided.