To prevent looseness regardless of the penetration of a solvent or the like for reducing the friction coefficient of lubricant or the like on the contact surface of a clamped screw.

A hard particle 2 whose particle diameter is 10 μm or less is adhered to a pressure reception screw surface 1a of a bolt 1, thus generating wedge effect to the pressure reception screw surface of internal threads by the hard particle 2 after clamping the bolt 1 for stopping looseness.