A crane comprising a luffing boom and a lifting cylinder, said lifting cylinder comprising a cylinder body mechanically connected to a structural element of the crane and a movable rod hinged on the luffing boom, wherein the movable rod is displaceable in the cylinder body between at least one deployed position and at least one retracted position in order to raise and lower the luffing boom between at least one raised configuration and at least one lowered configuration, said crane being characterized in that it further comprises a locking device adapted to cooperate with said lifting cylinder to mechanically lock the movable rod in a deployed safety position and thus block the luffing boom in a raised safety configuration, wherein said locking device comprises a spacer provided with a proximal portion hinged on the boom and with a distal portion supporting an abutment, wherein said spacer is pivotally movable on the boom between: - a release position wherein the spacer is offset vis-a-vis the lifting cylinder such that its distal portion is spaced apart from the lifting cylinder, authorizing the movable rod to be displaced in the cylinder body and to act on the displacement of the luffing boom; and - a locking position wherein the spacer is folded over the lifting cylinder such that the abutment is able to bear on the cylinder body; wherein a locking of the luffing boom in the raised safety configuration can be carried out according to the following locking sequence: - in a first phase or operating phase, the spacer is in the release position and the movable rod is free to be displaced in the cylinder body to act on the displacement of the luffing boom; - in a second phase or transitional phase, the movable rod is deployed to a deployed transition position, beyond the deployed safety position, and the spacer is displaced to its locking position by being folded over the movable rod; - in a third phase or locking phase, the movable rod is retracted from the deployed transition position towards the deployed safety position until the abutment bears on the cylinder body so that the spacer fixedly maintains the movable rod in the deployed safety position in order to lock the luffing boom in the raised safety configuration. - a release position wherein the spacer is offset vis-a-vis the lifting cylinder such that its distal portion is spaced apart from the lifting cylinder, authorizing the movable rod to be displaced in the cylinder body and to act on the displacement of the luffing boom; and - a locking position wherein the spacer is folded over the lifting cylinder such that the abutment is able to bear on the cylinder body; - in a first phase or operating phase, the spacer is in the release position and the movable rod is free to be displaced in the cylinder body to act on the displacement of the luffing boom; - in a second phase or transitional phase, the movable rod is deployed to a deployed transition position, beyond the deployed safety position, and the spacer is displaced to its locking position by being folded over the movable rod; - in a third phase or locking phase, the movable rod is retracted from the deployed transition position towards the deployed safety position until the abutment bears on the cylinder body so that the spacer fixedly maintains the movable rod in the deployed safety position in order to lock the luffing boom in the raised safety configuration.