The seat device, disposed on the floor panel in the cabin with the instrument panel, comprises the driver seat, the assistant seat and the rear seat, wherein the assistant seat is foldable and movable forward close to the instrument panel to be located in the stored position where the length of the folded seat is made short, the rear seat is foldable and movable forward to be located in the stored position, and the assistant seat in the stored position and the rear seat in the stored position provide the substantially continuous storage space which is formed by back faces of respective seat backs and of the assistant seat and the rear seat. Thus, both the large space and the roomy cabin for passengers can be improved.