Abstract: A joint member is used for positioning a first square tubular section made of aluminum or aluminum alloy and a second square tubular section made of aluminum or aluminum alloy with the sections' end portions butting against each other so as to weld the butt end portions together. The joint member includes an angle retainment portion and first and second anchorage portions. The angle retainment portion is applied onto the outer or inner surfaces of walls of the first and second square tubular sections, the walls intersecting each other with an angle equal to or smaller than 180.degree. when the first and second tubular sections are caused to butt against each other. The first and second anchorage portions branch off and extend from the angle retainment portion so as to fixedly hold the walls of the first and second square tubular sections, respectively, in cooperation with the angle retainment portion.