A seat device of a vehicle including a substantially flat floor surface substantially extending across a full cabin space of the vehicle, front row seats, center row seats and a rear row seat disposed in a longitudinal direction of the vehicle on the floor surface, a seat storage pan extending rearward the rear row seat and downward a level of the floor surface, the front row seats being disposed with a space, the center row seats including a plurality of seats in which at least one of the seats is movable in a lateral direction of the vehicle. When the rear row seat is received in the seat storage pan, a substantially flat and continuous surface of a substantially same level as the floor surface is formed rearward the center row seats to a rear end of the cabin space with a substantially full width of the cabin space. When the center row seats are disposed offset to one side of the vehicle with regard to the lateral direction, a substantially flat and continuous surface of a substantially same level as the floor surface is formed rearward the front row seats to a rear end of the cabin space. When the center row seats are disposed to produce a space at a central portion of the vehicle in the lateral direction, a substantially flat and continuous surface of a substantially same level as the floor surface is formed rearward the front row seats to a rear end of the cabin space at a central portion of the cabin space in the lateral direction.