To prevent play of fastened matter from occurring by restraining a screw from getting loose.

A bolt 7 is made to penetrate through the fastened matters 5 and 5 and a nut 9 is fastened via a washer 1 to a portion of the bolt 7 protruded from the fastened matter 5. The washer 1 comprises a saucer-shaped spring portion 2 with a diameter gradually enlarged from one end to the other end and a pressing portion 4 provided integrally with one end of the spring portion 2. When the nut 9 is fastened to the bolt 7, the washer 1 is axially pressed, so that a portion between one end and the other end of the spring portion 2 in the axial direction is curved and deformed, so that a repulsive force against a compressive force is generated in the spring portion 2. Since this repulsive force is added to pre-tension caused by a clamping matter 6, the pre-tension is increased to enable to prevent the screw from getting loose.