Abstract: A gas spring has a cylindrical housing and a piston rod mounted coaxially within it and sealingly extended out of same. The piston rod has a tapering cooperating with a seal in its pushed-in position. The seal is designed to be radially resilient and has an axially-operating radially resilient supporting ring which has webs extending parallel with the axis elastically movable radially to the axis, against which the seal applies. The purpose of this design lies in reducing the thrust force of the gas spring when the piston rod is pushed in, which should result at the same time in a reliable sealing in all operational positions.