A stopper device for the neck of a container, including: - a base which is globally tubular and adapted to be fastened to a neck of a container, - a cap which is globally tubular and movable relative to the base between a closed position, in which the cap sealably blanks the opening (16 1) of the base, while covering the base at least partially, and an open position, in which the cap is remote from the base to allow a flow through the opening of the base, said cap being moved substantially in the direction of the axis (X-X) of the base and opposite the neck of the container when it leaves its closed position to its open position, and - tamper-evident means (50, 60) intended to provide a visual indication of whether the cap has already been moved for a first time from its closed position to its open position, said tamper-evident means including a strand which, in an unaltered configuration, extends lengthwise along the periphery of the cap, and a hook, which is secured integral with the base, protruding toward the outside of the base, characterized in that the hook is adapted so that, when the strand is in the unaltered configuration thereof, the hook retains a running longitudinal portion of the strand, in a direction substantially parallel to the axis (X-X) of the base, so as to block the movement of the cap from its closed position to its open position, and in that a first longitudinal end of the strand is frangibly connected to the cap and is integrally provided with a tab for manually driving the strand so as to detach the first end of the strand relative to the cap, by breaking the frangible connection between them, then to move the running portion of the strand away toward the outside of the cap, by plastic deformation of a non-frangible connection between a second longitudinal end of the strand and the cap, until the strand reaches an altered configuration in which the cap is free to be moved from its closed position to its open position without the running portion of the strand being retained by the hook. - a base which is globally tubular and adapted to be fastened to a neck of a container, - a cap which is globally tubular and movable relative to the base between a closed position, in which the cap sealably blanks the opening (16 1) of the base, while covering the base at least partially, and an open position, in which the cap is remote from the base to allow a flow through the opening of the base, said cap being moved substantially in the direction of the axis (X-X) of the base and opposite the neck of the container when it leaves its closed position to its open position, and - tamper-evident means (50, 60) intended to provide a visual indication of whether the cap has already been moved for a first time from its closed position to its open position, said tamper-evident means including a strand which, in an unaltered configuration, extends lengthwise along the periphery of the cap, and a hook, which is secured integral with the base, protruding toward the outside of the base, characterized in that the hook is adapted so that, when the strand is in the unaltered configuration thereof, the hook retains a running longitudinal portion of the strand, in a direction substantially parallel to the axis (X-X) of the base, so as to block the movement of the cap from its closed position to its open position, and in that a first longitudinal end of the strand is frangibly connected to the cap and is integrally provided with a tab for manually driving the strand so as to detach the first end of the strand relative to the cap, by breaking the frangible connection between them, then to move the running portion of the strand away toward the outside of the cap, by plastic deformation of a non-frangible connection between a second longitudinal end of the strand and the cap, until the strand reaches an altered configuration in which the cap is free to be moved from its closed position to its open position without the running portion of the strand being retained by the hook.