Abstract: A climbing assist apparatus for oil derricks and the like comprises a cable which is attached to the worker and is trained over a sheave at the crown portion of the rig, then connected to a counterweight in order to remove slack from the cable as the worker is climbing. The sheave is keyed to a motor drive shaft which is free wheeling in one direction of rotation in response to advancement of the cable as the workman is climbing but will impose a controlled resistance in the opposite direction, this resistance being established through a hydraulic motor for the drive shaft and a hydraulic control circuit which includes a flow controller to resist the rotation of the motor in the opposite direction to that earlier described when the worker descends or should accidentally fall from the derrick.