A substrate processing apparatus capable of improving thin film uniformity on a substrate by controlling the position of a substrate supporting apparatus includes a plurality of reactors, wherein each of the reactors includes a substrate supporting apparatus; a ring surrounding the substrate supporting apparatus; and an alignment device for moving the substrate supporting apparatus, wherein the ring is installed such that one surface of the ring comes in contact with the substrate supporting apparatus as the substrate supporting apparatus moves and the ring is movable by a pushing force of the substrate supporting apparatus.