A pivot-mounting device has a lower nut (4) is fixing a bolt (2) to an object (A), and an upper nut (3) having a boss (32) rotatably supporting a rotatable member (B) is tightened on the bolt (2). A lower nut (4) includes an engagement recess (41) into which the boss (32) can be fitted with the outer peripheral surface of the boss (32) and the inner peripheral surface of the engagement recess (41) each being a straight cylinder shape. The boss outer peripheral surface (32) is slightly eccentric relative to a female thread hole (3a).