A seat-back frame of a seat-back comprises at least a pair of right and left side frames, a pressure receiving member disposed between the side frames, and wires for connecting the pressure receiving member to the side frames, respectively; wherein the wire is connected to the side frames through link members which are operable relative to the side frames, respectively, and wherein the link members are so configured that the wire is urged toward a forward side of the seat-back frame by tension springs.