Seat back frame for vehicle

A seat back frame (20), mainly including a first back frame (23) which is formed in a hollow angular column shape and which includes a first side plate portion (23c) forming one side surface of the first back frame (23), a first wall portion (23d) and a second wall portion (23e), which are formed by bending end portions of the first side plate portion (23c) so as to be positioned at a front side and the rear side of the seat, respectively, a second side plate portion (23f) and a third side plate portion (23g), which are obtained by bending a side end portion of the first wall portion (23d) and the second wall portion (23e) towards the rear side and the front side of the seat, respectively. The third side plate portion (23g) is overlapped on the second side plate portion (23f) so as to be in contact with each other, and connected therebetween at an overlapped portion in a vicinity of a bent portion between the first wall portion (23d) and the second side plate portion (23f).