To provide a joint member prevented from projecting large on the outside of a first member and a second member when used to join the end parts of the cylindrical first and second members opened at the joined ends.

The joint member is provided with a joint splice plate 41 of plate shape formed with fitting holes 41a in a plurality of positions, and screw members for thread-fastening the mutually joined end parts of the joint splice plate 41 and first and second members 44, 45 at a right-angled direction to the length direction of the first and second members. A stepped nut 47 and a headed bolt 50 are used as the screw member, wherein the stepped nut 47 comprises a small diameter part 47a fittingly fixed into the fitting hole of the joining splice plate by press-fitting or the like and has a length formed shorter than the plate thickness of the joint splice plate, and has a threaded hole 47b in the axis part, and the headed bolt 50 is fastened to the threaded hole of the stepped nut by inserting the tip part of a screw shank 50a through the first and second members and the joint splice plate inward from the outside of the first and second members.