The present invention relates to a water softening device including: a resin chamber which has an ion exchange resin and softens hard water passing through the ion exchange resin; and electrodes which are arranged by placing the resin chamber therebetween and apply voltages to the resin chamber so as to soften the hard water, and which regenerates the ion exchange resin, wherein the ion exchange resin is a slightly acidic cation exchange resin and/or a weakly alkaline anion exchange resin. The present invention provides the water softening device capable of easily regenerating the ion exchange resin and repeating the softening-regenerating without using chemicals or the like while maintaining the performance of softening water, thereby enabling a continuous use thereof.