According to an aspect of the present disclosure, there is provided a substrate treating apparatus comprising: a vessel part having a substrate treatment region formed therein and including a supply port through which a treating fluid is supplied to the substrate treatment region and an exhaust port through which the treating fluid is exhausted from the substrate treatment region; a fluid supply unit configured to supply the treating fluid to the substrate treatment region; an exhaust unit configured to exhaust the treating fluid from the vessel part. The exhaust unit comprises: a main line connected to the exhaust port; an extension line branched from at least one of first and second nodes of the main line and including at least one of a first orifice or a first check valve to control an exhaust speed; and an auxiliary line branched from a third node of the main line, where an orifice and a check valve are not formed. During a first process time, the treating fluid is discharged through the extension line, and the treating fluid is not discharged through the auxiliary line, and during a second process time, the treating fluid is discharged through the auxiliary line.