A seat back framework for use in a seat back of a vehicle seat, wherein said seat back includes an upper side and two lateral sides, comprising: an upper frame member disposed in the upper side of said seat back; a first lateral frame member disposed in one of said two lateral sides of said seat back, said first lateral frame member having an upper region; a second lateral frame member disposed in another of said two lateral sides of said seat back, said second lateral frame member having an upper region; a first shoulder receiving portion defined in said upper region of said first lateral frame member so as to project from said first lateral frame member in a direction forwardly of the seat back framework; a second shoulder receiving portion defined in said upper region of said second lateral frame member so as to project from said second lateral frame member in a direction forwardly of the seat back framework; said first and second shoulder receiving portions being adapted for receiving a first and second shoulder portion of a seat occupant of the vehicle seat, respectively, when a back portion of said seat occupant is displaced backwardly and upwardly under inertia to and along said seat back in case of rear-end collision, thereby preventing said back portion of said seat occupant against further backward and upward displacement prior to said back portion being moved close to said upper frame member, characterised in that each of said first and second shoulder receiving portions has a recessed area defined therein, said recessed area having a surface formed substantially in conformity with localized upper and back regions of each of said first and second shoulder portions of said seat occupant, and wherein said recessed area is to be buckled or deformed by an excessive great load being applied thereto from said each of said two shoulder portions in the case of rear-end collision, thereby absorbing an impact to be imparted to said first and second shoulder portions. an upper frame member disposed in the upper side of said seat back; a first lateral frame member disposed in one of said two lateral sides of said seat back, said first lateral frame member having an upper region; a second lateral frame member disposed in another of said two lateral sides of said seat back, said second lateral frame member having an upper region; a first shoulder receiving portion defined in said upper region of said first lateral frame member so as to project from said first lateral frame member in a direction forwardly of the seat back framework; a second shoulder receiving portion defined in said upper region of said second lateral frame member so as to project from said second lateral frame member in a direction forwardly of the seat back framework; said first and second shoulder receiving portions being adapted for receiving a first and second shoulder portion of a seat occupant of the vehicle seat, respectively, when a back portion of said seat occupant is displaced backwardly and upwardly under inertia to and along said seat back in case of rear-end collision, thereby preventing said back portion of said seat occupant against further backward and upward displacement prior to said back portion being moved close to said upper frame member,