A washing machine includes: a steam generator for generating steam; a circulation pump for pumping circulation water discharged from a tub and re-supplying it into a drum; a spray nozzle for spraying steam generated from the steam generator and the circulation water pumped from the circulation pump into the drum; and a back-current preventing branch unit connected to the steam generator by a steam supply line, connected to the circulation pump by a circulation line, and connected to the spray nozzle. With this structure, circulation water circulated by the circulation unit and steam generated from the steam generator are sprayed to the laundry through one spray nozzle, so that a system can be simplified and a fabrication cost can be reduced.