To provide an airtight sash frame, requiring for no labor, at a low cost by a method wherein a frame member is disposed on the back side of the side edge part on the indoor side of the sash frame, and an airtight material adhered to the frame member is attached to the back of the side edge part on the indoor side of the sash frame.

The outdoor side formed of aluminum of a sash frame 1 is pointed to the outside of a room and mounted on a column and a beam arranged in a wall body. Thereafter, a frame edge member 2 is inserted in the back side of the side edge on the indoor side of the sash frame 1 and by deforming the fin-shaped protrusion of an airtight material 3 and adhering it to the frame member 3, mounting is effected. Further, the sash frame 1 is fixed at the frame member 2 by a screw 4. Further, the airtight material 3 is molded by using soft polyvinylchloride resin and molded integrally with the indoor side of the sash frame 1 formed of rigid polyvinylchloride resin. A gap between the sash frame 1 and the frame member 2 is brought into an airtight state by the airtight material 3. This constitution prevents the occurrence of vapor condensation to the internal part of the wall body due to penetration of steam in a room at a low cost.