a washing chamber;

top and bottom nozzles injecting water in the washing chamber;

a sump provided under the washing chamber to store the water;

a pump pumping the water stored in the sump;

a supply pipe adjacent to one side of the pump wherein the water pumped by the pump flows in the supply pipe;

upper and lower pipes leading the water to the top and bottom nozzles, respectively; and

a valve assembly connecting the supply pipe to the upper and lower pipes to selectively open/close the upper or lower pipe using a pressure of the pumped water, wherein the valve assembly comprises a first guide portion and a second guide portion that are coupled together to form a valve assembly housing which is separate from the pump, and wherein an inlet hole formed in the first guide portion is coupled to the supply pipe, wherein first and second outlet holes in the second guide portion are coupled, respectively, to the upper and lower pipes, and further comprising a bail that moves along a passage formed between the first and second guide portions to selectively open and close the first and second outlet holes.