Disclosed is a substrate treating apparatus comprising a wafer chuck on which a substrate is placed, an injector unit on a side of the wafer chuck and injecting process gases that include a first gas and a second gas, and a gas supply unit supplying the process gases to the injector unit. The gas supply unit comprises first and second gas supply sources that respectively accommodate the first and second gases, first and second gas supply lines that respectively connect the first and second gas supply sources to the injector unit, and first and second heating units that are respectively disposed on the first and second gas supply lines. The first heating units disposed on the first gas supply line have a density per unit length greater than the density per unit length of the second heating units disposed on the second gas supply line.