A seat device includes a seat cushion where a sitting person is seated, and a seatback configured to support the upper body of the sitting person. The seatback includes a seatback frame, a seatback pad placed on a front face of the seatback frame, and a seatback cover covering a surface of the seatback pad. A plurality of stretch airbags is provided in a part of the seatback at a position corresponding to the lumbar part of the sitting person, and the stretch airbags are configured to inflate and press a surface of the seatback to a direction approaching the sitting person. The stretch airbags are placed to overlap each other in a thickness direction of the seatback such that the seatback pad is sandwiched between the stretch airbags.