A seat back frame for the vehicle seat, includes a pair of side frames that are disposed on both sides in a seat width direction; and a supporting plate that has both ends connected to a bottom section of each of the side frames, wherein the supporting plate is at least disposed along an interval between a first height that corresponds to an upper part of a lumbar vertebra of an occupant seated in the seat and a second height that corresponds to a lower part of the lumbar vertebra, and curves in a manner such that, in a cross-section along with a vertical direction, the supporting plate bulges forward along a line from the first height to the second height.