A telescopic actuator comprising a cylinder having a structure for coupling the cylinder to a first external element a rod mounted to slide telescopically in the cylinder along a sliding axis and including a structure for coupling it to a second external element and a lead screw mounted to rotate in the cylinder about the sliding axis and extending inside the rod to co-operate with a nut secured to the rod, such that rotating the lead screw causes the rod to slide. There also is a drive structure for driving the lead screw in rotation and a retention structure for axially retaining the lead screw. The retention structure holds a bearing of the lead screw captive in an axial direction and is arranged to retain the bearing of the lead screw with axial clearance suitable for absorbing movements imparted to the rod relative to the cylinder.