A frame structure for use in a vehicle seat back

A seat back in a vehicle rear seat provided before a trunk includes a seat back frame structure in which a peripheral frame member is arranged along the periphery of a substantially rectangular panel frame member, and a reinforcing pipe frame member having opposite ends thereof coupled to an upper part and a lower part of the peripheral frame member and having an intermediate part formed to pass an external-force receiving portion of the panel frame member where an external force resulting from a possible movement of a luggage placed in the trunk is received. There can be provided a frame structure for the vehicle seat back having an improved strength against an external force exerted resulting from the movement of the luggage placed in the trunk.