To provide a mischief preventive fitting of a bolt member for a building.

A mischief preventive fitting 1 to prevent nuts 21, 22 from being loosened and removed by mischief is constituted of a sleeve 2 on which a protruded part 5 to project in the radial direction on an inner peripheral surface of a cylindrical body 4 to cover an outer peripheral part of the nut, a connecting part 6 on which a stepped part 9 inserted into the sleeve and engaged with the protruded part and female screw to be screwed on a bolt 17 are formed and a fastening member 3 having a head part 7 projected outside from the sleeve which is integrally formed on the connecting part through a shearing part 8. Thereafter, a plastic deforming part 11 to flow in and connect by plastically deforming between the bolt and the nut when it is screwed in the bolt is formed on the connecting part, and the head part is cut off and removed from the shearing part when fastening force exceeding connecting force of the plastic deforming part.