To provide a slip-off prevention screw capable of ensuring a large positioning adjustment margin.

A slip-off prevention screw comprises: a screw knob part 1 whose outer diameter is greater than an inner diameter of a screw hole 12 on a panel 11; an end screw part 3 whose outer periphery is provided with a male thread 3a that engages with a female thread 16 formed on a sub-rack 14, and whose outer diameter is smaller than the inner diameter of the screw hole 12 on the panel 11; a slip-off prevention screw part 4 which is arranged closer to the screw knob part 1 than the end screw part 3, and whose outer periphery is provided with a male thread 4a that engages with a female thread 13 formed on an inner periphery of the screw hole 12 on the panel 11; and a screw shaft 5 which is provided between the slip-off prevention screw part 4 and the screw knob part 1, and whose shaft diameter is smaller than the inner diameter of the screw hole 12 on the panel 11.