PURPOSE: To make coupling easy and stabilize coupling portion strength by putting part of a shaft into one end of a thin pipe, forming the recesses and projections of predetermined shapes at the outer periphery of a piled-up portion by means of rolling work, and conducting the recess and projection fitting of thin pipe inner periphery to shaft outer periphery.

CONSTITUTION: The recess and projection fitting of thin steel pipe 11 inner periphery to shaft 12 outer periphery is conducted via a process in which piling up is carried out by putting the small 11 diameter portion 12a of the shaft 12 into one end of the thin steel pipe 11 and the recesses and projections of predetermined shapes are formed at piling up portion A outer periphery by means of rolling work using a pair of rolling dies 20. This method requires no special skill, and processing precision can be obtained stably, and the easy coupling of the thin steel pipe 11 to the shaft 12 is realized, and at the same time the strength of a coupling portion is stably obtained, and production efficiency is improved. Also, by changing the shapes of the pair of rolling dies 20, rotary strenth, bent strength, pulling strength or the like between the thin steel pipe 11 inner periphery and the shaft 12 outer periphery can be changed, and optimum coupling strenth can be obtained accurately.