A seat back frame assembly, comprising a substantially U-shaped pipe member having a horizontal base and a pair of vertical legs extending upwardly from the horizontal base and terminating at a pair of upper ends, a transverse member having a first horizontal portion welded at the opposite ends to the upper ends of the pipe member, a first vertical portion depending from the first horizontal portion to extend along one side of the pipe member and having a lower end continuing to a second horizontal portion lying beneath the first horizontal portion between the vetical legs of the pipe member, and a second vertical portion depending from the second horizontal portion along the other side of the pipe member, each of the first and second vertical portions having opposite edge portions welded to the legs of the pipe member, the first horizontal portion having a pair of transversely spaced holes, the second horizontal portion having a pair of holes which are respectively aligned in vertical direction with the holes in the first horizontal portion for receiving headrest receptacles.