PURPOSE: To improve the production efficiency, and to reduce the cost by elongating or compressing a spiral shear key material, bringing it into contact with the peripheral surface of a steel pipe, and subsequently, fixing the shear key material to the steel pipe by means of welding.

CONSTITUTION: A spiral shear key material 1 made of steel is constituted by forming in advance a shear key material such as a band steel, etc. so that the spiral inside diameter is slightly larger than the outside diameter of a steel pipe 2, and also becomes a prescribed spiral pitch. Subsequently, the steel pipe 2 is passed through the inside of the shear key material 1, and thereafter, the diameter is reduced by drawing both ends of the shear key material 1, and it is brought into contact with the outside surface of the steel pipe 2 by keeping a necessary spiral pitch. Fixing jigs 9, 10 are fixed to both end parts of the shear key material 1 and engaged with both ends of the steel pipe 2. Next, the shear key material 1 is welded and stuck to the outside surface of the steel pipe 2, and the fixing jigs 9, 10 are removed, by which a desired product is obtained. It is unnecessary to finish the shear key material 1 with high accuracy, and it can be worked in a short time, therefore, the production efficiency is improved and the cost is reduced.