PURPOSE: To prevent moisture condensation and cloth peeling by interposing a moisture condensation preventing member between a sash frame and a wall bed material through a locking part, and pressing a cloth bonded to the wall bed material by a cloth presser provided on the moisture condensation preventing member.

CONSTITUTION: After a cloth 23 is bonded to a wall bed material 21 to the position where the edge part can be pressed by a cloth presser 6, a sash frame 10 is then mounted on the wall bed member 21. A moisture condensation preventing member 1 is inserted into a space S between the frame 10 and the bed 21, and a locking groove 5 is engaged with the locking 13 of the frame 10. The moisture condensation preventing member 1 is interposed and mounted between the frame 10 and the bed 21 in this state, and the cloth 23 is pressed by the cloth presser 6. Thus, a heat bridge caused in the contact part between the sash frame and the wall is eliminated, moisture condensation on the wall can be prevented, and the cloth peeling caused by a secular change can be also prevented.