To sufficiently reduce a surface pressure working on a belt even if tension is applied to the belt.

This manufacturing method consists of a first drawing process b1 for forming a first stage projection part T1, a second drawing process b3 for protruding the first stage projection part T1 to form a second stage projection part T2, a third drawing process for protruding the second stage projection part T2 to form a third stage projection part T3, a piercing process punching a long hole corresponding part in the third stage projection part T3, a surface pressing process d for removing a shear edge part T3b, a forming process e for forming an opening edge 23a in a circumference wall part 23, a restriking process f for rounding the cross section of the circumference wall part 23, a double-sided projecting bar forming process g for forming projecting bars 611a, 611b from a restruck part 24, and a separating process j separating a belt mounting metal fitting.