VEHICLE SEATBACK FOLDING DEVICE

A vehicle seatback folding device includes: a cushion bracket; a back side frame rotating on the cushion bracket; a spring mounting bracket coupled to rotate integrally with the back side frame around a hinge-coupling part; a return spring for applying, to the back side frame, elastic restoring force for rotating the back side frame in the folding direction of a seatback; and a reverse spring supported in a state in which a first end portion is caught by the spring mounting bracket and a second end portion is caught by a first spring support end.