Provided is a gas exhaust apparatus for expelling a gas in a treatment space of a wafer treatment apparatus to outside, the gas exhaust apparatus including a main exhaust line connected to the treatment space, and an auxiliary exhaust line having an end connected to the main exhaust line to supply an external air current to the main exhaust line, wherein an automatic closer is disposed at another end of the auxiliary exhaust line to close the other end of the auxiliary exhaust line in a specific situation.