Seat-back frame for vehicles

The purpose of this invention is to simplify the structure for softening the shock of a rear-end collision. The lower portion of each of its right-side and left-side members 3, which are made of sheet steel, include a plurality of holes 7 and 8 in which fastening bolts 11 and 12 are inserted so as to connect the side members 3 with an external member. The fastening bolt 11 is capable of contacting the hole brim of a hole, and by installing such a fastening bolt 11 in all of the holes, or in all of the holes but one, the shock of a rear-end collision is softened.