To provide a cover variable in a removal difficulty level in accordance with the site of use and the purpose for use by attaching a cover on heads of a cross slot head screw and hexagon socket head screw to inhibit the removal of the screws by a work tool.

The head of the cross slot head screw has a columnar shape. In a lateral side of the columnar screw head, a stopper groove 7 is formed deeper toward a screw-head-end direction and a groove tilted in a screw top end direction is formed. A cover mounted in the screw head is made up of a spring material. A plurality of claw-shaped stoppers 2 which opens in a cover cap direction and toward an inside of the cover is provided on a lateral side of the cover made up of the spring material. When inserted into the screw head, the claw-shaped stopper 2 is locked on a lateral side of the groove of the screw head. Further, the cover cap is holed and the hole is closed by a soft-material circular plate from inside to enable the soft-material plate to be holed by an electric drill. Part of the soft-material circular plat is formed in a sheet and thereby the screw head can be easily sealed. When the sheet-like portion is broken to loosen the screw, therefore, a seal broken state can be recognized. As a result, a burglarproof screw cover having a removal difficulty level variable in accordance with the site of use and the purpose for use is obtained.