PURPOSE: To prevent deterioration in the function and strength as a waterproof roof, etc., while minimizing a repairing area of local damage in the repair of a metal waterproof membrane used for a roof, etc.

CONSTITUTION: Seam welding of waterproof face members is made at rising sections 2 of both side edges to form a metal waterproof membrane, and it is cut off so as to surround a damaged part (d). For the rising sections 2, they are cut off so as to cross seam welding lines 3 from the upper part to the lower part, and the lower parts of the seam welding lines 3 are cut off. Between the rising sections 2 and 2 of each of the waterproof face members 1 is cut off in the horizontal direction so that a specific uneven step (a) occurs between adjacent waterproof face members 1 and 1, and the sphere of repair is eliminated. The cut end of each of the waterproof face members 1 is bent by required width (b) to form a horizontal rising section 6, it butts into a horizontal rising section formed in a new waterproof face member and seam welding is made. After that, seam welding of both side edge rising sections of the existing and new waterproof face members is made, and repairs are completed.