SEAT BACK FRAME FOR AUTOMOBILE

A seat back frame for automobile includes a first side frame and a second side frame that are arranged apart from each other in a vehicle width direction, an upper frame that connects an upper end portion of the first side frame and an upper end portion of the second side frame, and an upper bracket that is attached to the upper end portion of the first side frame and guides a seat belt. The first side frame includes a columnar member made of an aluminum alloy extruded material and having a closed cross-section portion in a cross-section perpendicular to a vehicle vertical direction, and a plate-shaped reinforcing member made of high-tension steel, joined to the columnar member, and extending to a vehicle rear side of the columnar member.