A water softening module has a case body which includes cover members secured to their respective ends of a cylindrical case. A pair of electrodes are provided in the case body. A fibrous medium is located in contact with a water-outlet-side face of the electrodes. The fibrous medium has a stacked structure constituted of a first fiber layer and a second fiber layer, which are electrically conductive. The first fiber layer is positioned in contact with the upstream side of the second fiber layer, and the first fiber layer is positioned in contact with the downstream-side face of the electrodes. The specific surface area of the first layer is smaller than that of the second fiber layer.