The invention provides a vehicle seat capable of preventing a mounting mechanism of a support structure for supporting the back of a sitter from being large, and a seat frame of the vehicle seat. A seat frame (F) of a vehicle seat (S) is provided with side frames (15) which are positioned at left and right sides of a seat backrest frame (1) and extend to upper and lower directions. The side frames(15) are provided with side parts (15a) extending along the side part of the seat (S), rear parts (15c) protruding from the rear end surfaces of the side parts (15a) to the inner side of the seat (S), and support parts (20) and (22) erected between the left and right side frames (15) and used for bearing the backrest load of a sitter. The support parts (20) and (22) are provided with connecting parts for connecting the side frames (15), and when the connecting parts and the side frames (15) are in a fixed state, the connecting parts are mounted at rear parts (15c) of the side frames (15).