To allow fastening to be performed easily as well while pressing in a shaft center direction.

In an antitheft screw 1 in which a head 3 is provided at one end of a shaft part 2 formed with a male thread 2a and three locking parts 31 are formed on the head 3 at circumferential intervals, the head 3 is formed in a hemispherical shape having a curvature radius gradually decreased toward the vertex, and each locking part 31 is formed by an arched vertical surface 31v as a first surface when viewed from the side and an arched horizontal surface 31h as a second surface when viewed from the above, and the vertical surface 31v of each locking part 31 is formed correspondingly to a part of each side of an equilateral triangle when viewed from the above. Further, at one end of the locking part 31, a projection 32 is provided. Accordingly, only a fixture having a recess for avoiding the projection 32 can be fitted to the locking part 31.