A seat frame structure includes a seat cushion frame, a seat back frame, and a connecting bracket connecting the seat cushion frame to the seat back frame. The seat cushion frame includes a first beam portion having an internal space in at least one of a left/right side edge portion. The seat back frame includes a second beam portion having an internal space in at least one of a left/right side edge portion. The connecting bracket includes a first arm portion inserted into the internal space of the first beam portion and connected to the first beam portion and a second arm portion inserted into the internal space of the second beam portion and connected to the second beam portion.