PURPOSE: To reduce entrance of a high-humidity low-temperature air into a closet and a portion under a floor and to enable prevention of the formation of dew and production of mould, by providing a temperature humidity sensor, an electronic circuit board for controlling a motor, and a shutter.

CONSTITUTION: An electronic circuit board 24 for controlling a motor inputs an open air temperature signal T and an open air humidity signal R from an integrally-formed temperature humidity sensor 21 at every set time interval (t), and compares the signals with a reference temperature T0 and reference humidity R0 previously stored in the electronic circuit board 24 for controlling a motor. In the case of the reference temperature T0 < the open air temperature signal T and the reference humidity R0 > the open air humidity signal R, a ventilating fan is actuated, and a motor 1 is kept in an energized state while the conditions are satisfied, and when the conditions are not satisfied, the motor 1 is brought to a stop. This extremely reduces a ratio of a high- humidity open air and a low-temperature open air entering a place under a floor and a closet, resulting in reduction in a rate of dew formation in a closet and prevention of production of mould due to formation of dew.