A cap of a tube container having an automatic sealing structure, which more reliably performs an airtight function, prevents liquid ingredients in a nozzle from drying, safely protects the nozzle in a physical way, prevents gel-phased medical ingredients from being in contact with the outside air to the maximum extent possible, thus allowing the medical ingredients to be preserved for a longer period of time, and which is constructed so that the cap is integrated with the container, thus eliminating the risk of loss resulting from the separation. A cone which is secured by each locking protrusion inserted into a guide slit is inserted into a body as the locking protrusion moves, so that a nozzle hole is opened by an anti-drying unit and contents are discharged through an ejected nozzle.