PURPOSE: To provide a moistening device which performs necessary and enough moistening suitable to an atmospheric condition at each room without needing a large floor area, according to a method wherein a suction port and a supply port are formed in a ceiling surface, a duct, intercommunicating the suction port and the supply port, a blower for blast located in a duct, and a moistening device are provided, and a temperature sensor, coupled to the blower and the moistening device, is situated in a space to be moistened.

CONSTITUTION: When humidity in a room is decreased during heating, a signal is inputted to an ultrasonic moistening device 9 and a blower 10 from a humidity sensor 13 for operation. In case the water tank of the ultrasonic moistening device 9 is short of water, an electromagnetic valve 12 is opened, water is supplied through a feed water pipe 11, and upon completion of supply, the electromagnetic valve 12 is closed. Simultaneously with operation of the blower 10, the ultrasonic moistening device 9 is also actuated, spraying is effected to the interior of a duct 8, the air in the duct 8, communicated through the suction port 5 with the supply port 7, is mixed, and the moistened air is blown into a room. When humidity in the room is increased, the humidity is detected by the humidity sensor 13 to bring the ultrasonic moistening device 9 and the blower 10 into a stop.