A thin film manufacturing system, wherein a stage for placing a substrate thereon is disposed within a vacuum reactor and a gas head for supplying a film forming gas to a central area on a top face of the vacuum reactor is arranged so that the gas head is opposed to the stage. A cylindrical sleeve member is disposed and comes in close contact with a side wall of the stage to surround a periphery of the stage. The height of the stage can be established at the position where the volume of a second space formed below the stage and connected to a vacuum discharge means is larger than that of a first space formed above the stage, in such a manner that an exhaust gas is isotropically discharged from the first space without causing any convection current therein through the interstice between the sleeve member and an inner wall surface constituting the reactor.