Zoom optical system comprising diffractive optical element and imaging device having the same

A zoom optical system has, in order from an object: a first lens group G1 having positive refractive power; a second lens group G2 having negative refractive power; a third lens group G3 having positive refractive power; and a fourth lens group G4 having negative refractive power, wherein the mutual distance between the lens groups G1 to G4 change upon zooming, and one of the third lens group G3 and the fourth lens group G4 includes at least one diffractive optical element PF.