The stopper (2) engages with a ring-shaped neck in a press fit in a container (1) and has a circular bottom section which seals the container opening, and a head section which rises above the container and encompasses a slide (3) that extends through the center of the head section, the rim of the head section having a maximum diameter that does not exceed the external diameter of the container opening. The stopper is characterized in that the slide can be pushed against the force of a spring device in one direction over the rim of the container and, when released, returns to its retracted initial position as a result of the spring resistance. The stopper cannot be removed from the container by small children and is therefore considered childproof.