To provide a tamperproof cap, which has a tamperproof function, which facilitates attachment work to a container with a hinge cap, and which is easily openable by a bit of force.

The tamperproof cap has a virgin cover fitted on the outside of the cap attached to the container. The virgin cover is equipped with an annular cover top and an outer peripheral wall, and a flap is provided at the lower end of the outer peripheral wall. In the outer peripheral wall, tear grooves are engraved at regular intervals, and the portion sandwiching the tear grooves forms a cutting part. A connecting piece is extended to a circumference upper end in the cutting part, and a pull ring is connected to the connecting piece.