PURPOSE: To couple the fitting member to the shaft member by rushing a pair of punch member into both sides of the fitting member fitted to the shaft member, and allowing a shaft member metal to flow plastically to the fitting member.

CONSTITUTION: The fitting member is fitted to a metallic shaft member 33, and thereafter, a pair of punch members 41 are rushed simultaneously into a position which becomes the vicinity of both end faces of the fitting member 35 in the shaft member 33. By this rush-in a shaft member metal is allowed to flow plastically to both the end faces of the fitting member 35. Subsequent, by a projecting part 43 formed by this plastic flow, the fitting member 35 is coupled to the shaft member 33.