Disclosed herein is a washing machine that performs washing using bubbles. The washing machine may include an air bubble unit to generate air bubbles in detergent water using external air naturally introduced thereinto by pressure difference caused when the detergent water passes therethrough, a water tub having an introduction port to allow the detergent water containing the air bubbles to be introduced thereinto, and a washing tub rotatably provided in the water tub, the washing tub having a plurality of through-holes having a size less than the introduction port such that the air bubbles rise to a surface of the detergent water contained in the water tub.