PURPOSE: To achieve the low power consumption and unattended antenna station, by constituting dry air in antenna power feeding, when the internal pressure in the antenna power feeding section is a prescrived value or less.

CONSTITUTION: Water vapor in a feeder 3 moves upward due to the difference of density based on the difference with molecular weight with air and flows to a dryer 4 through a pipe 9. The water vapor is absorbed in drying agent, dried air is fallen down due to the difference of specific gravity with the water vapor and flows to the feeder 3. When a pressure in the feeder 3 drops due to leakage or the like, external air is dehumidified with a liquid hygroscopic agent 7 and is stored in a space 6a as dried air and fed to the inside the feeder 3 via the drier 3.