A zooming imaging optical system includes, in order from an object side to an image side, at least: a first lens group having positive refractive power; a second lens group having negative refractive power; a third lens group having positive refractive power; a fourth lens group having positive refractive power; a fifth lens group having negative refractive power; and a sixth lens group. During zooming, the distance between adjacent lens groups changes. During focusing from an object at infinity to a close object, the fifth lens group moves along an optical axis toward an imaging surface side. The second lens group includes, in order from the object side to the image side, at least: a 2a-th lens group; and a 2b-th lens group having negative refractive power. Image stabilization is performed by displacing the 2b-th lens group perpendicularly to the optical axis. The optical system satisfies a predetermined conditional expression.