PURPOSE: To easily provide a straight line serving as the reference for external angles of a wall by applying tension to a building material (cord) which is suited to form wall external angles in straight lines and to finish the external angles in straight lines by following the straight line.

CONSTITUTION: A cord 1 for forming wall external angles comprises a strip of net 2 and an untwisted cord 3 which is bonded to one of the long sides of the net 2; in this case, notches 5 may be cut in the net 2 at equal intervals from the other long side of the net 2 and in the direction perpendicular to the cord 3. To form external angles of a wall using the cord 1, both ends of the cord 3 under tension are secured to the upper and lower sides of a building, and a fixative is applied to the cord 3 to form the cord 3 into a rectilinear rod, and a wall material is applied along the cord 3, thus forming the external angles.