A seat back structure includes a seat back panel, a cushion member disposed on a seating surface side of the seat back panel, and an intermediate member inserted into a space between the panel and the cushion member. The panel is comprised of a metal plate member and formed with an embossed portion protruding at the seating surface side, and a bead portion protruding at an opposite side from the embossed portion at a position surrounding the embossed portion. The intermediate member has a lower specific gravity than the cushion member and a higher hardness than the cushion member. The intermediate member is formed with a contacting portion contacting the embossed portion and a concaved portion denting toward the cushion member at a position corresponding to the bead portion. A space is formed between the concaved portion and the panel, at a position adjacent to the contacting portion.