To secure the joining strength between a cylindrical body and a disk body subjected to friction stir joining, and to reduce the load on a tool for friction stir joining.

A probe 34 rotating clockwise is buried in the rim 12 so that the axis line L1 of a rim is separated from the axis line L2 of a tool 30 for friction stir joining. At this time, preferably, the amount of the first shoulder part 36 to be buried is controlled to 1/2 to 3/2 of the thickness T1 of the rim 12, and on the other hand, the amount of the second shoulder 38 to be buried is controlled to ≤1/2 of the thickness T1 of the rim 12. In this state, the rim 12 is rotates counterclockwise (to the direction of the arrow X) so that the tool 30 for friction stir joining is relatively revolvingly moved along the outer circumferential wall of the rim 30 with the first shoulder part 36 as the head.