An object is to provide a zoom lens system that can realize high image quality, a large aperture and a small size simultaneously and that can optically compensate blur of the image due to hand blur, vibration or the like, an imaging device and a camera. The present invention relates to a zoom lens system, in order from the object side to the image side, comprising a first lens unit having positive optical power, a second lens unit having negative optical power, a third lens unit having positive optical power and a fourth lens unit having positive optical power, wherein variable magnification is achieved by moving at least three lens units in an optical axis direction, focusing is achieved by moving the fourth lens unit in the optical axis direction, blur of the image is compensated by moving the third lens unit in a direction perpendicular to the optical axis, and at least one of a condition (1): 0<(|.DELTA.L|f.sub.W)/(f.sub.TIM)<10.times.10.sup.-2 and a condition (2): 0.005<(|.DELTA.L3|f.sub.W)/(f.sub.TIM)<0.15 (here, Z=f.sub.T/f.sub.W>8.0) is satisfied, an imaging device and a camera.