To provide a humidifier in which the propagation of various bacteria and the precipitation of carbonate are suppressed by reforming city water to be supplied to humidifying means.

Hypochlorous acid generating means 20 has a pair of electrodes 22a, 22b spaced from a cation exchange screen 23 and an electrolytic cell 21 provided with the cation exchange screen 23 and the electrodes 22a, 22b for introducing city water. Voltage is applied to the electrodes 22a, 22b for electrolyzing the city water, whereby the city water containing hypochlorous acid generated in the city water on the side of the electrode 22a to which the polarity of an anode is applied is supplied to the humidifying means 10 for humidifying air. Thus, the hypochlorous acid is supplied to the humidifying means 10 in the form of removing cations which form carbonate.