Abstract: So that the boom does not have to be oriented horizontally to change the crane configuration, a remotely controlled double locking device is mounted at the front end of each intermediate telescoping member slidably mounted between the boom base and the inner telescoping member. Each intermediate telescoping member can thus be locked according to choice with the inner telescoping member or another intermediate telescoping member, or with both that telescoping member and a top piece of an extendable rod of an extending device which increases the boom length. This double locking mechanism comprises two double piston mechanisms positioned opposite each other each with an exterior lock bolt operable by an exterior spring-loaded or hydraulic adjusting cylinder and mounted inside this exterior lock bolt an interior lock bolt operable by an interior spring-loaded or hydraulic adjusting cylinder.