To form a reduced diameter part and a serration in a single process and easily and accurately form the serration in a hollow pipe having the serration in the inner surface of the reduced diameter part.

A die 7 for reducing the diameter of the end part of a pipe material 12 is disposed on the outside of the pipe material 12. A core metal 8a formed in an irregular shape for serration formation is disposed in the end part of the pipe material 12 on the side where the die 7 is disposed. A load is applied to the other end part of the pipe material 12 to push the pipe material 12 into the die 7 so as to move the core metal 8a in the same direction of the pressing direction for the pipe material 12. Thus the reduced diameter part and the serration can be formed at the end part of the pipe material 12.