To improve productivity and material yield of a part to be used as a pillar-like part for a skeletal structure portion of a vehicle and the like or a part to be possibly joined parallely with different kinds of members for a floor and the like.

This is referred to a method to joint coiled steel plates in the tailored blank method to manufacture a steel belt for press forming by jointing several different kinds of steel belts. In concrete, more than two kinds of slit steel belts, for example, a steel belt A, a steel belt B, a steel belt C, are joined together by such a joining method as a laser, mash seam welding and the like so as to make the joining lines in a longitudinal direction of the steel belts.