PURPOSE: To improve the extent of productivity by forming a flange part into such a form as having plural noncontinuous circular parts left behind with one another after partially notching the circumference of a circular plate, and constituting it to weld a fitting part between this circular part and a connecting hole.

CONSTITUTION: In an internal gear builtup body 10, a circular part 14c of a flange member 14 is fitted in a connecting hole 12b of an internal gear 12, and a fitting part, where both come into contact with each other, is welded, whereby both are coupled together. Since this weld takes place for the circular part 14c (for example, three spots) only, production efficiency is improved as compared with the case where the whole circumference is welded. In addition, since the circumference of the flange part 14 is notched, weight is also lightened in comparison with the case of circularity.