To secure the waterproof function without spoiling the appearance, by using a common drip cap member regardless of one or two finish tiles arranged along the external wall of the girder side.

A ridge face piece 4 and a batten plate 5 are arranged in close proximity to the wall at the uppermost stage of tiles 3 and fixed thereto, at the nearby position of the wall between the roof tile Y of the first floor and the external wall K of the girder side of the second floor. Thereafter, a substrate member 62 of a drip cap is arranged along a fitting member 9 and the batten plate 5 fixed to the external wall K to fix them with nails. Then, the upper member 61 of the drip cap arranged to correspond to the notch (k) of the external wall K is fixed with nails to the external wall K in the state that the upper end of the vertical piece of the substrate member 62 of the drip cap where the vertical piece of the upper member 61 is arranged along the fitting member 9, is covered within a certain range, regardless of one or two finish tiles 3.