A hood (4) in a tower (3) receives air having absorbed heat released from a corrugated rib tank (2). The hood (4) is set above the corrugated rib tank (2) of a transformer (1) being installed on a foundation in the interior of a tower and transforming electric power generated by an electric generator. An exhaust duct (6), which discharges the air having absorbed heat released from the corrugated rib tank (2) and flowing into the hood (4), is provided to the interior of the tower (3) so as to be connected to the hood (4) and extend upward up to the upper portion of the tower (3).