PURPOSE: To provide a structure of structural material joined part which is strong and stable in joining strength and easy in joining work, and can accommodate metal fittings and bolts used for joining so as not to disturb the joining work, and can easily join another structural material in a horizontal or vertical direction near a joined part.

CONSTITUTION: One of three faces of a cylindrical joining hardware 1 having right-angled isosceles triangle-shaped longitudinal section is horizontally or vertically set, and the end of a structural material 2 is abutted on one of two other faces and tightly attached to that. An inclined face 3 inclining at 45 degrees to the perpendicularity of the joining hardware 1 provided at the end of the structural material 2 on one side, and an inclined face 3 inclining at 45 degrees to the perpendicularity of the joining hardware 1 provided at the end of the structural material 2 on the other side are mutually abutted to join both the inclined faces 3.