Abstract: A device for folding and unfolding a hinged boom pivotally mounted atop a telescopic crane mast, in which a cable is secured to the mast and passes over pulleys located, in sequence, at the top of the lower mast section, the bottom of the upper mast section, the top of the upper mast section and on the first boom section adjacent the hinge and thence to another anchor point adjacent the free end of the second boom section. Preferably a spacer strut is placed at the hinge and as the mast telescopes downwardly torque in the cable causes the second boom section to pivot, at the hinge, so that when telescoping is complete the mast and both boom sections are in a coplanar parallel relationship.