PURPOSE: To easily engage a non-locking part with a locking part and to hold joining strength by forming the locking part at one edge of a joining part, forming a part to be locked concerned to this locking part at the other edges of the joining part and engaging the locking part with the part to be locked after a plate stock is bent.

CONSTITUTION: Since locking part 5D is formed at one edge of the joining part and a part 5G to be locked is formed at the other edges of the joining part, the part 5G is engaged easily and simply with the locking part. Therefore, welding gap in a conventional butted part need not be adjusted. Further, when the joined edge part is worked by a laser beam at least, the engaging state between the part to be locked and the locking part is good, the butting accuracy is improved and the strength of the joining part can be improved by welding or brazing the joined edge part.