PURPOSE: To prevent damage or fall of a blocking member so as to enable nut rotation drive by means of a manual device by forming a loose piercing part, which has smaller diameter then that of the male screw part and a flattened outer circumference face between the male screw part and the blocking member.

CONSTITUTION: A fixed-length male screw part around which a nut 56 makes screwing motion is provided in the middle of a fastening rod 1 and a loose piercing part 4 which has smaller diameter than that of the male screw and a flattened outer circumference face is formed between the make screw part 3 and a locking member 58. Therefore at releasing fastening, after a nut 56 makes screwing motion upward in relation to the fastening rod 1 and is released from the male screw part, it moves to the loose piercing part 4 so as to decrease rotation torque rapidly. Thereby releasing of the nut can be sensed easily. An energizing means 5 having expansion force is attached between the nut 56 and the blocking member 58. Therefore impact force of the nut 56 exerted on the blocking member 58 at loosening/releasing can be damped by its elastic repulsion force so as to evade drop and damage of the blocking member 58.