A back frame structure of a vehicle seat, the back frame structure including: a pair of side frames extending in an upper and lower direction; and an upper frame that connects upper end sides of the side frames in a bridging manner, the upper frame including: a main body part having a substantially inverted U-shaped cross-section opened downward; and a cover member attached to the main body part so as to close at least a part of an opening end side in the cross-section of the main body part.