Abstract: An arrangement for erecting and dismounting an elongate object having one end articulated to a foundation is used, e.g. for erecting power transmission line supports into vertical or substantially vertical position. The arrangement comprises a chassis which is stationary during the installation of an object, a boom having one end thereof articulated to the chassis and a load gripping member mounted for displacement towards the distal end of the boom. In addition, the arrangement is provided, at the distal end of the boom, with an additional boom support articulated thereto which is disposed on the ground during the installation of an object. This additional boom support enables a considerable reduction of power input of means effecting the displacement of the load gripping member carrying the object due to a re-distribution of forces developed during the installation of the object.