To permit removal of rain water or the like from a roof by forming a water drain hole at the roof portion of a cover curtain attached to a frame, and providing a drain passage connected to this water drain hole and communicated to the outside.

A cover curtain attached to posts 10, 10 forming an internal space is equipped with a rectangular curtain 14 covering above the internal space and a plurality of side surface curtains 18, 20 connected to the end portion. And an almost circular opening for inserting a rotor shaft of a helicopter to be housed is formed almost at the central position of the roof curtain 14, and a cylindrical member 30 made of polyester canvas is attached to the peripheral edge portion. Moreover, a plurality of water drain holes 48 are formed in the roof curtain. And on the rear surface of the roof curtain 14, two drain passages 50 extended respectively from the lower position of the water drain hole 48 to the front curtain or rear curtain 18. Each drain passage 50 is constituted by attaching a groove with a V-shaped cross section made of polyester canvas to the rear side of the roof curtain 14 by thermal welding, and the water drain hole 48 is communicated to the drain passage 50 and water is drained from the drain hole 54.