Abstract: A pressure adjustment apparatus includes a storage tank storing a gas for the chamber with an outlet, a first supply line supplying the gas from an external line to the storage tank, a second supply line supplying the gas from the storage tank to the chamber, a discharge line discharging the gas from the chamber using the outlet of the chamber, and a controller controlling valves at the first, second, and discharge lines. The discharge line includes first and second valves connected to each other in parallel at an end portion of the outlet of the chamber, and a third valve connected to the end portion of the outlet of the chamber. The controller opens the first and second valves to discharge the gas from the chamber, and opens the third valve after a predetermined amount of time after the opening of the first and second valves.