PURPOSE: To obtain products uniform in accuracy at high efficiency by sending three bandlike steel strip making two of them parallel and another from a direction at right angles to the above, and working the bandlike steel strip successively and bringing them adjacent to each other at a specified position.

CONSTITUTION: The first and second bandlike steel strips 5, 7 are sent out in parallel to the same direction by material sending mechanisms 13, 14, and the third steel strip 9 is sent out by a material sending mechanism 15 so that it overlaps the first steel strip 5 intersecting at right angles. Next, the steel strip 9 is cut to a specified length and bent to U-shaped, and steel strips 5 and 9 are welded and formed to ring-shape with both ends of the steel strip 9 facing outwards. This overlapped steel is cut and shifted so that steel strips 5, 7 are linearly positioned and overlapped. The steel strips 5, 7 are welded under this state of overlapping and the steel strip 7 is bent to the direction of the steel strip 9, and the steel strip 7 is cut to a specified length.