The present disclosure relates to an apparatus for automatically locking a container, which includes: a cylindrical housing: a top plate installed on the top of the housing; a bottom plate installed under the housing; an elevation unit installed to move up and down in the housing; a locker installed to rotate left and right to lock and unlock a container; a guide guiding up-down movement and rotation movement of the locker; a first elastic supporting member elastically supporting upward the elevation unit; and a second elastic supporting member elastically supporting upward the locker. Accordingly, the present disclosure provides an effect that a container is automatically locked or unlocked by its own weight when it is loaded or unloaded, so it is possible to safely transport heavy containers always in a locked state and it is possible to prevent malfunction or poor function of the locker.