To form both a fitting part and a part fitted to the fitting part in a cylindrical member in a cross-sectional noncircular shape, and to very tightly fit both in lock nuts having a female screw part threadedly engaged with male screw parts of male screw materials and the fitting part fitted to the end part vicinity of the cylindrical member in a joining structure of the cylindrical member and the male screw materials capable of moving the male screw materials in the shaft direction to the cylindrical member and fixable to an optional position by inserting a part of the male screw materials into the cylindrical member.

The fitting part 13 of the lock nuts 2L and 2U can rotate to the female screw part 12. The fitting part 13 sufficiently fastens the lock nuts 2L and 2U even in a nonrotatable state to the cylindrical member 3, and the fitting part 13 is moved in the shaft direction, and can be sufficiently fitted to the cylinder member 3.