To provide a mechanism for suppressing dew condensation, which prevents the progress of corrosion of an inner surface by urging ventilation inside a steel pipe, without replacing a tail end material on the uppermost top of a steel tower.

A cover body 31 is attached via a collar 32 to a flange portion 30 which is provided on the steel pipe 29 on the uppermost top of the steel tower; and a vent hole 33, which is formed with a diameter larger than that of the cover body 31 and which provides ventilation with the inside of the steel tower by attaching a cap material 34 for covering the cover body 31 from above, is formed on the upper portion of the cover body 31. Since a drainage plate is provided on the lowermost portion of the steel tower, exhaust air is discharged to an upper portion of a main column material 11 from a lower portion thereof by negative pressure generated inside the main column material 11.

COPYRIGHT: (C)2010,JPO&INPIT