Disclosed herein is a water softening apparatus including an electrosorption unit to adsorb foreign matter contained in water with electrical attraction, a preprocessing unit having a preprocessing chamber which is connected with an external water supply source and is provided with a filter to filter out foreign matter contained in water transferred from the external water supply source, and a cleaning solution supply unit having a cleaning solution storage chamber which stores a cleaning solution to be supplied to the electrosorption unit. Since any one of the water transferred from the preprocessing unit and the cleaning solution transferred from the cleaning solution supply unit is selectively transferred to the electrosorption unit by a valve, a pump to inject the cleaning solution and the like are unnecessary.