A seat device for a chair having a lumbar support or a seatback is provided. A lower portion of the lumbar support (or seatback) is formed as a shaft having an external teeth portion for positioning pin lugs of a base and fixed blocks. A movable block is joined with one of the fixed blocks. An elastic member is positioned between inner holes of the external teeth portion and an internal teeth portion of the movable block. The fixed blocks are secured by outer covers. A lifter is pivoted to the outer cover secured with the movable block. The lumbar support (or seatback) is separated into a plate including a ladder-type groove and sliders and a pad jointed with a board on the back having a latch member and sliding grooves. A pull bar extends from the board. The angle and height adjustable lumbar support (or seatback) is therefore achieved.