PURPOSE: To join the steel material to the aluminum-base material with high joint strength by the weldbonding method.

CONSTITUTION: Aluminum or an aluminum alloy with 2-20μm thickness is applied on the joining face of steel material 10 which is one material to be joined and a hot setting adhesive 30 of an epoxy system, etc., is applied thereon. This steel material is superposed on aluminum-base material and spot-welded together and then, the steel material and the aluminum-base material are integrated into one body by hardening of the adhesive 30. Accordingly, since a hard and rugged alloy layer is formed on a spot weld zone, welding strength is increased and a joint having resistance to stress added before the adhesive is hardened is obtained. In addition, adhesive strength itself is increased as compared with the case where Zn-base material is applied.