When a seat (3) (FIG. 6A) on which a wax layer (7) is formed via a melting reaction layer (5) is brought into contact with a head (2) and heated and pressed in this state, a melting reaction layer (6) forms below the wax layer (FIG. 6B). When electric current application and pressing are continued from this state, a wax which has not reacted in the wax layer (7) in the formation of the melting reaction layer (6) is discharged from between the melting reaction layers (5) and (6). When electrical current application and pressing are further continued from this state, the two melting reaction layers (5) and (6) diffuse each other. The result is that a ternary alloy bonding layer (10) containing Fe, Al, and Zn, which constitute the melting reaction layers (5) and (6) is formed between the seat (3) and the head (2) (FIG. 6D).