To precisely and efficiently form outer teeth and inner teeth to a cylindrical part in a synchronized phase by pressing a mandrel with tooth grooves to the peripheral faces respectively arranged to the inside/outside of a cylindrical part of a cup shaped stock, and a form rolling die having a rotation axis roughly parallel to the mandrel while they are synchronously rotated.

Outer teeth of a male tooth shape and inner teeth of a female tooth shape are formed to the cylindrical part 1a of a cup shaped stock 1, a cup shaped gear is produced. A mandrel 3 having tooth grooves on its peripheral face is fitted/inserted into the inside of the cylindrical part 1a, further, a form rolling die 7 having tooth grooves on its peripheral face with an rotating axis roughly parallel to the mandrel 3 is fitted to the outside of the cylindrical part. By pressing the form rolling die 7 as well as the mandrel 3 on the cylindrical part 1a while synchronously rotating both of them and pressurizing the cylindrical part 1a with the tooth groove of the mandrel 3 and the tooth groove of the form rolling die 7, the outer teeth and the inner teeth are formed.