PURPOSE: To reduce gear cutting processes and to improve the efficiency by forming a raw material both of the ends at which gear portions are machined, and later gear-cutting the central portion thereof to form a worm portion.

CONSTITUTION: A raw material 2A is formed according to the pressed power forming method of power metal, gear portions 22, 23 having gear items identical to spur gear portions of a product are formed one of half portions in the longitudinal direction and the other half portion. The raw material 2A is sintered and normalized and the central portion thereof is cut to be mated to the outer diameter of a worm portion 11 and also a through hole 14 is formed. The outer diameter portion of the worm portion at the central portion is gear-cutted to form the worm portion. According to this method, it is eliminated to gear-cut both of the end portions 12, 13 and a gear-cutting portion to be machined is to be only the worm portion 11 so that the manufacturing efficiency is improved.