To solve such a problem that because air in an object region is discharged after simply comparing a measured humidity with a reference humidity in an old ventilation system when a humidity difference obtained by subtracting a humidity of open air from a humidity in the object region is lower than a predetermined reference humidity, the humidity under the floor is undesirably raised by the open air, while high humidity air under the floor is rightly discharged to the outside when the humidity difference is higher than the reference humidity.

In a ventilation system, operation of a ventilation unit is subjected to wireless remote control to generate an air flow by alternating air supply and air discharge at regular intervals.