AUTOMOTIVE-STRUCTURAL-PART JOINT STRUCTURE, AUTOMOTIVE STRUCTURAL PART, AND AUTOMOTIVE-STRUCTURAL-PART MANUFACTURING METHOD

An automotive-structural-part joint structure 1 according to the present invention is formed by bending one metal sheet, includes a top portion 3 and a pair of side wall portions 5, is provided at an end part of an automotive structural part 110 in a longitudinal direction, joins to an automotive structural part 120 in an intersecting direction, and includes a pair of vertical rib portions 9 standing upward from both side ends 3b of the top portion 3, and an outward-directed flange portion 11 continuously formed along a side edge on an end part side where joining to the automotive structural part 120 occurs, each of the vertical rib portions 9 is formed by overlapping a part of the metal sheet, and the flange portion 11 is constituted by a flange portion adjacent to top 11a extending upward from the top portion 3, a flange portion adjacent to side wall 11b laterally extending from each of the side wall portions 5, and a vertical-rib flange portion 11c laterally extending from each vertical rib portion 9.