Abstract: A quick-acting closure with a retaining-ring, which enables fixture and detachment of a shell and a cover of a pressure vessel by the retaining-ring comprising, a circular groove formed on the inner face of the shell of the pressure vessel, and holes formed through the shell at a plurality of places in the circumferential direction of the circular groove, and a rod inserted through the holes and connected with the retaining-ring, wherein retaining-ring is positioned to be freely moved to the radial direction of the shell, the shell and the cover are fixedly installed by the retaining-ring engaging with the circular groove of the shell and the cover when the retaining-ring is moved forward to the inside direction of the diameter of the shell, and the retaining-ring is retracted into the circular groove to make the shell and the cover detachable when the retaining-ring is moved backward to the outside direction of the diameter.