PURPOSE: To ensure high workability, a short construction period, high safety, and high mounting accuracy, and further ensure the high strength, durability and adiabatic quality of an area around a sash after installation, as well as the easy replacement work of the sash.

CONSTITUTION: A metal frame material 4 is fitted along the inner edge of the open section 2 of a concrete building wall 1, as an integral part thereof. The anchor member 7 of the periphery of a sash 6 is fitted to a plate member 5 mounted on the metal material 4, thereby fastening the sash 6. As the anchor member 7 and plate member 5 are tightened to each other with a screw 8, the fixing position thereof is freely changeable or detachable from each other. In addition, a gap between the periphery of the sash 6 and the metal frame material 4 is filled with foaming mortar 9, thereby completing an installation work.