A crane having a telescoping boom whose sections, are arranged in a base boom that can telescope individually, in and out, after disengaging locking pin connections that are secured in the respective moved out or moved in positions by locking pins. A guide profile head is arranged at an end remote of the articulation of the safety locking unit to the inner end of the base boom. To lengthen the boom without substantially changing the telescopic system itself, the guide profile head is detachably fastened to the safety locking unit. An additional guide frame, whose length is dimensioned corresponding to the length of the telescoping boom that has been expanded by additional sections inserted in the telescoping boom, is mounted in place of the guide profile head, and that a guide profile head can be arranged at the free end of the guide frame.