To provide a stable friction stir joining portion, an efficient tacking method as a tacking method for both joined members to be implemented before friction stir joining, and a friction stir joining method using the method.

The joining portions of members 10, 20 to be joined are butt-arranged in a position enabling friction stir joining to be performed. A tacking member 40 is arranged in a position superimposed on the surface of the abutted members 10, 20. Then, the members 10, 20 and the tacking member 40 are joined by a stud welding method or a friction welding method.