Abstract: Provided is a water ionizer which can detect a detection target installed at a predetermined position of a genuine filter to recognize that a genuine filter is loaded, which makes it possible to raise the reliability of the water ionizer and to extend the lifespan of the water ionizer. The water ionizer capable of recognizing a genuine filter, which has a water purifying filter for filtering foreign matters contained in original water, includes a sensor that is operated by a detection target attached to a proper position of a filter case of the water purifying filter; and a controller that checks whether a genuine water purifying filter is loaded or not, based on the sensing result of the sensor, and then stops the operation of the water ionizer when a genuine water purifying filter is not loaded. The water ionizer may further include a guide unit that guides the water purifying filter such that the water purifying filter is loaded at a predetermined position of the water ionizer.