PURPOSE: To improve finishing appearance and weather resistance while simplifying the execution of works by installing furring strips for sticking a sizing onto the external wall surface of a building into opening sections, inserting U-shaped resin-coated channel members into the furring strips and covering the end faces of the furring strips.

CONSTITUTION: Furring strips 10 are mounted on the surface of a previously executed external wall A. A sheet, in which a resin film is formed onto the surface of an aluminum base material as a channel member, is formed in an approximately U shape, thus forming a channel member 40. The channel member 40 is inserted to the end secion of the furring strips 10, thus covering the end face of the furring strips. Accordingly, the finishing appearance of the furring strips 10 becomes good while the execution of works can be simplified.