To provide a washer capable of allowing a user to visually confirm whether a screw is completely fastened or not when the screw is fastened, and further to confirm whether fastening axial force is sufficiently introduced or not.

A projecting knob 3 projecting from a washer main body 1 and positioned in the middle of a projecting claw portion 2, is brought into contact with a fastened member face 11, the more the screw is fastened, the more the projecting claw portion 2 projects from the washer main body 1, so that the projecting claw portion 2 starts its plastic deformation at a thinned base portion to be bent upward and turned over. The more the screw is fastened, the higher a tip 4 of the projecting claw goes up, and the tip 4 of projecting claw is deformed and bent upward to a visually confirmable degree in a state that the screw is completely fastened. In this state, the complete fastening of the screw can be confirmed.