The apparatus includes a plurality of process chambers having treatment spaces configured to process the substrate in the treatment spaces, and an exhaust unit to exhaust gas from the treatment space. The exhaust unit includes a plurality of individual exhaust pipes directly connected to the treatment spaces in one process chamber or the plurality of process chambers, a main exhaust pipe connected to the plurality of individual exhaust pipes, a pressure reducing member installed in the main exhaust pipe to reduce pressure of the treatment space, and a damper member mounted in each of the individual exhaust pipes to adjust an amount of gas exhausted through the individual exhaust pipe. The damper member includes a first damper to adjust an amount of gas exhausted from the treatment spaces, and a second damper disposed downstream of the first damper to buffer a pressure change caused by adjusting the first damper.