<p>Provided is a seat back frame for a vehicle seat equipped with a pair of side frames that are disposed on both sides in the widthwise direction of the seat and a supporting plate that has both ends connected to the bottom section of each aforementioned side frame, wherein the aforementioned supporting plate is at least disposed along an area between a first height that corresponds with the upper portion of the lumbar vertebra of a passenger seated in the aforementioned seat and a second height that corresponds to the lower portion of the aforementioned lumbar vertebra, and curves in a manner such that, in a vertical cross section of the seat, the supporting plate protuberates forward along a line from the aforementioned first height to the aforementioned second height.</p>
