A drum washing machine capable of washing a helmet includes a pulsator installed on a bottom of a drum and configured to be rotatable independently of the drum. A fixing device is configured to detachably fix an object to be washed having a three-dimensional shape to an inner lower side of the drum. A processor is configured to control a water storage process for storing water in the tub in an amount, in which at least a part of the pulsator is submerged, and to control a pulsator to agitate the water inside the tub by rotating the pulsator in a state in which the drum is stopped to maintain a lower position of the object to be washed.