<p>The present invention relates to an opening and closing device of an automatic cap for a liquid container comprising a container (10); a cap (20) screwed with an inlet of the container (10); and an opening and closing member (30) discharging contents or closing the container by being installed in the container (10) by passing through the inlet of the container (10) and the cap (20). The present invention can automatically discharge the contents in the container without separating the cap which is a cover of the container and close the container. The present invention also simply seals the cap in order to prevent the contents from being leaked.</p>
