Provided is an apparatus for treating a substrate using a supercritical fluid. The substrate treating apparatus includes a housing, a support member disposed within the housing to support the substrate, a supercritical fluid supply unit in which the supercritical fluid is stored, a supply tube connecting the supercritical fluid supply unit to the housing to adjust an amount of supercritical fluid supplied from the supercritical fluid supply unit into the housing, and a vent tube branched from the supply tube to discharge the supercritical fluid remaining in the supply tube. A switching valve opening or closing the vent tube is disposed in the vent tube.