A control unit comprises a calculation unit, a determination unit, and a motor rotation control unit. The calculation unit calculates the rate of change in water level, which indicates the amount of change in water level per a predetermined period of time, on the basis of the result of sensing by a water level sensor in connection with a water supply stroke. The determination unit determines whether laundry having a waterproof property is contained in a drum or not on the basis of the rate of change in water level during the water supply stroke calculated by the calculation unit. When it is determined that laundry having a waterproof property is contained in the drum, the motor rotation control unit controls the operation of a driving motor such that the drum is rotated at a predetermined number of rotations or less during the dewatering stroke.