At a side portion 22 of a seat back frame, not only does a rear first extending portion 52 bend and extend from a frame side plate portion 30 toward a seat back inner side at an obtuse angle, but also, in a vicinity of a central portion of a rear flange portion 50, a rear second extending portion 54 bends and extends from the rear first extending portion 52 further toward the seat back inner side. Therefore, even if a relatively large load toward a rear of a vehicle acts on the seat back frame and compressive stress is generated at an intermediate portion of the rear flange portion 50 in a heightwise direction of a seat back, it is difficult for cross-sectional collapsing to arise, and the load can be effectively supported at the frame side plate portion 30. There can be provided a seat back frame for a vehicle which can suppress an amount of bending deformation at the time of a rear collision, without leading to an increase in weight.