To provide a new type washer and a washer-fitted tightening tool.

The washer is composed of a shank having a first supporting surface to be brought into contact with a nut, a second supporting surface to be brought into contact with an object to be tighten, and an additional turning resistance surface to be brought into contact with the outer periphery of a bolt. When the nut is turned, the turning of the bolt is prevented by the frictional resistance between the bolt and the shank produced at the turning resistance surface, but the axial movement of the bolt is possible. In addition, the turning of the shank is prevented by the frictional resistance between the shank and the object to be tighten, produced on the second supporting surface. Further, the frictional resistance applied to the first supporting surface is set to be smaller than that on the second supporting surface so as not to turn the shank with the turn of the nut.