To prevent the corrosion of screws and the electric erosion of frame materials by disposing in section a screw hole connected to a vertical frame in a hollow part outer side for discharging water on an upper expected piece and forming a screw hole in the side opposite to the hollow part in the lower side of a room outer side rail.

For example, an upper drain hole 7 held between a rail 3 closest to a room outer side and a rising piece 6 is moved over the rail so as to discharge rainwater to a hollow part 4. An upper drain hole 7 adjacent to the upper drain hole 7 in section discharged the rainwater passed over the rising piece 6. Then, A lower drain hole 9 for discharging the water in the hollow part 4 is a lower direction of formed in a lower expected piece 5 positioned in the lower part of the hollow part 4 and facing the hollow part 4. Further, a water stop block for partitioning the space of the hollow part 4 in the longitudinal direction is made of a air permeation material and housed tightly in the hollow part 4. Thus, the contact of water passing in the hollow part 4 with a screw hole 18 is prevented, and permeation of the water to a vertical frame 17, screw corrosion and the electric erosion of the lower and vertical frames 1 and 7 are prevented.