Provided is a substrate treating apparatus. The substrate treating apparatus comprises: a housing having a treating space therein; a spin head for supporting and rotating a substrate in the treating space; and a chemical supply unit having an injection nozzle for supplying a chemical to the substrate which is supported by the spin head, wherein the injection nozzle comprises a nozzle body, and wherein the nozzle body comprises an inner space for receiving a chemical and minute holes which are connected with the inner space for discharging the chemicals to downward.