To maintain the lifetime of products long, and while to lower the manufacturing cost by forming a device of a first member at the predetermined length which includes a female screw part, and other members which includes a male screw and an intermediate screw between the female screw and the male screw, and bonding the first member and the second member with each other in the axial direction.

An extension rod is formed into a tubular member, which is formed of a first member 1, a second member 2 and a third member 3. A tip of the first member 1 is formed with a female screw part 4, and the third member 3 includes a male screw part 5. The first member 1, the second member 2 and the third member 3 are bonded to each other by the frictional pressure-contacted in the axial direction at pressure-contact positions C1, C2. Since the extension rod is formed of plural members 1, 2, 3 provided in the axial direction, a steel material of high quality similar with the conventional one can be used for the first member 1, in which breakdown and abrasion is generated by the use on a relatively short time, namely for a member, which includes at least a female screw 4 at a tip thereof. Consequently, lifetime of products can be maintained long, and the manufacturing cost can be lowered.