PURPOSE: To prevent the deflection of a sill and, at the same time, to firm the fixation of an opening panel and to facilitate mounting work by providing a reinforced bearing member under the external wall frame sill, and fixing the external wall frame on the foundation through it.

CONSTITUTION: A reinforced bearing member 4 bearing an external wall frame sill 20 in a position of a sash is provided to under the external wall frame sill 20 in a position to which the sash 2 of an opening panel 1 is mounted. The fixing work of the reinforced bearing member 4 to the top end of the foundation 3 and an anchor bolt 5 can be made through a gap between the external wall frame sill 20 and foundation top end.