A delivery device (1) for delivering a stent device (3) that is expandable from a radially reduced, delivery configuration to a radially expanded, deployed configuration. A retaining sheath (4) is disposed over the stent device for maintaining the stent device in the delivery configuration. A pull line (13) to be pulled upon is provided to retract the retaining sheath in a rolling manner such that the retaining sheath is folded back on itself to provide a radially inner sheath (7) of the retaining sheath, a radially outer sheath (8) of the retaining sheath and a fold portion (9) therebetween. The pull line is moveable by pulling thereon to move the outer sheath over the inner sheath and thus to move the fold portion axially relative to the stent device to retract the retaining sheath from over the stent device to release the stent device for expansion to the deployed configuration. The pull line extends axially along the stent device and joins the retaining sheath substantially at or beyond an axial end of the stent device in a pre-retracted configuration of the retaining sheath. The retaining sheath is made of a cold drawn plastic at least along the path of travel of the fold portion in retracting the retaining sheath from over the stent device.