A seat device that is capable of improving body pressure distribution during traveling is provided. In a seat device including a seating seat, in both of end portions in the seat width direction of the seating seat, at positions interposed between the bottom plate and a cushion member of the seating seat, turning plates are provided. The parts of the cushion member, where the turning plates are provided between the same and the bottom plate, constitute turning parts that turn around edges thereof on the width direction inner sides as base points, as the turning plates turn. In the cushion member, slits are formed at boundary positions between the turning parts and a non-turning part, that is, a part other than the turning parts.