WASHING MACHINE

A washing machine includes a washing tub, a water tub, a drive unit, a feed-water unit, a drain unit, a water softening unit, a pH increasing unit, a pH decreasing unit, and a control unit. The water softening unit is disposed between the feed-water unit and the water tub, and is filled with a weak acid cation exchange material having weak acidic cation exchange groups with a pH from 7.5 to 14 at point of zero charge. The pH increasing unit increases the pH of washing water, and the pH decreasing unit decreases the pH of the washing water. The control unit performs the following operations: controlling the pH increasing unit to increase the pH of the washing water while the washing water is being fed; introducing the washing water with the increased pH to the water softening unit to decrease the hardness of the washing water; introducing the washing water with the decreased hardness to the washing tub; controlling, after the washing water is fed, the pH decreasing unit to decrease the pH of the washing water to a value of 5.5 to 7.0; and introducing the washing water with the decreased pH to the water softening unit.