The inventive concept provides a substrate treating apparatus. The substrate treating apparatus includes a chamber providing a treating space; and a fluid supply unit supplying a treating fluid to the chamber, and wherein the fluid supply unit includes: a supply tank storing the treating fluid; a supply line connecting the supply tank and the chamber; and a plurality of valves installed at the supply line, and wherein any one valve among the plurality of valves is provided as a safety valve, and wherein the safety valve is opened after confirming that the chamber has been switched to a closed state when supplying the treating fluid from a tank to the chamber.