A seat configuration member and a vehicle seat employing the seat configuration member are provided that are capable of covering reclining mechanism components and maintaining a high quality external appearance of the vehicle seat, and are moreover capable of achieving a reduction in the number of components. A lower side coupling and fixing portion disposed on a seat width direction outer side of a seat back board that is made from resin is integrally formed with an attachment portion that is L-shaped in plain view. A side airbag device is attached to a horizontal wall portion of the attachment portion. A seatback pad and a cover are mounted to the seat back board configured as described above, and the seat back board is assembled to side frames of a seatback frame.