PURPOSE: To provide the subject humidifier capable of suppressing deterioration of steam-generating heater of a water storage tank by carrying out water- discharge operation of the water storage tank of a humidifier in starting or stopping of operation.

CONSTITUTION: A water discharge circuit 35 is connected to a water storage tank of a humidifier 2 and a water discharge valve of the water discharge circuit 35 is opened for only a definite time in operation of operating switches 51 and 61 and water in the water storage tank is discharged through the water discharge circuit. Thereby, the concentration of hardness component dissolved in stored water in a water storage tank is lowered by supplemental city water and the hardness component can reduce an amount contacted to a steam- generating heater.