The humidifier includes a humidification section which vaporizes water to produce humidified air, and a fan which produces in an air passage an air flow delivering the humidified air to the outside. The humidifier further includes a sterilized water producing section which produces sterilized water, an ultrasonic irradiator which produces sterilizing mist through ultrasonic irradiation of the sterilized water, an auxiliary passage through which the sterilizing mist is delivered to the outside, and an operation switching mechanism. The operation switching mechanism is switched between a first operation mode in which the air passage and the auxiliary passage communicate with each other to introduce the sterilizing mist into the air passage, and a second operation mode in which communication between the air passage and the auxiliary passage is blocked.
