The washing machine includes a tub, a drum, a plurality of balancing units moving along the circumference of a front side or a rear side of the drum in order to reduce imbalance caused by concentration of laundry when the drum rotates, a vibration sensor sensing a vibration amount of the tub, and a controller moving the plurality of balancing units according to the vibration amount of the tub, measured by the vibration sensor. The controller controls a drum motor to rotate the drum at a constant rotation speed, moves the plurality of balancing units in the same rotation direction to minimize the vibration amount of the tub, measured by the vibration sensor, and thereafter moves the plurality of balancing units in different rotation directions to minimize the vibration amount of the tub, measured by the vibration sensor, thereby reducing imbalance.