Dishwasher having steam washing function and dishwashing method

A steam/water mixed dishwasher using steam and water together, and, more particularly, a dishwasher and dishwashing method of achieving improvement in washing performance and efficiency via direct steam injection to dishes. The dishwasher includes a body (1) containing a dishwashing tub (2), at least one dish basket (28a,28b) disposed in the dishwashing tub and adapted to receive dishes therein, a steam generator (60) to generate steam by heating wash water, and steam injection nozzles (70) to inject the steam generated from the steam generator. The steam injection nozzles are disposed at the same height as a lower surface of the dish basket. The dishwashing method includes injecting steam from a number of the plurality of steam injection nozzles by opening a number of the plurality of control valves (64), to thereby maintain an injection pressure of the steam generated from the steam generator.