To provide an additional tightening device for constantly maintaining a joining condition at the time of initial construction, so that looseness can not occur in a bolt and a fastening nut, in mainly joining a construction wood.

A bolt 2 for penetrating a joining member and also a fastening nut 3a for fastening the joining part are provided, a helical spring 4 for constantly imparting torque in a fastening direction is provided on the nut 3a, and moreover a reenergizing nut 3b for imparting given torsional stress to the helical spring and a locking nut 6 for fixing the reenergizing nut are provided on the helical spring.