A washing machine includes a water tub; a water supply device to supply water into the water tub; a detergent supply device to supply detergent; a circulating device to circulate the water supplied into the water tub; a drum mounted in the water tub to receive clothes therein; a motor to rotate the drum; and a control unit to control the water supply device and the detergent supply device so that the water and the detergent are supplied into the water tub, bubbles of detergent dissolved water are generated, and washing of functional clothes is performed using the bubbles by varying a drive operation rate of the motor stepwise for a washing period.