To securely realize a lock to the bolt of a nut.

A hexagon nut 2 is inserted in a clearance at the nut retaining part 13 of a washer 1 (a). With the hexagon nut 2 formed integrally with the washer 1, the washer and the hexagon nut 2 are gradually tightened to a bolt 33 from the outside of the nut retaining part 13 of the washer 1 by using a wrench or a spanner (b, c). The tooth part 11 of the washer 1 is held by a tightened body 4 and the hexagon nut 2 and pressingly collapsed, extended in the direction of the shaft of the bolt 3 and brought into a state in which the bolt 3 is clamped from the periphery (d, e). Since the washer 1 is locked to the bolt 3 and the rotation of the hexagon nut 2 is stopped by the nut retaining part 13 of the washer 1, the hexagon nut 2 is also locked to the bolt 3 in this state.