A foldable crane, preferably a truck crane, that includes a rotatable column, to which a lift arm is pivotally mounted through an attachment point, and a lift arm and an articulated arm that are pivotally connected with each other via attachment point, and a hydraulic system that operates between the lift arm and the articulated arm, and that contains two cylinders, which are positioned symmetrically with respect to the longitudinal axis of symmetry of the lift arm and articulated arm and attached laterally with respect to the lift arm and articulated arm at each side of the crane, characterised in that each piston hydraulic cylinder includes a belonging set of levers, and the two sets of levers are connected with each other by a linking element via pivotal attachment which connects both lever elements with the piston hydraulic cylinder, and wherein each of said sets of levers consists of a first lever element that has two ends (5a, 5b) and a second lever element that has two ends (6a, 6b), and the first lever element and the second lever element are pivotally connected with each other through the first ends and via attachment point and the first lever element is pivotally connected with its end with the lift arm via attachment point and the second lever element is pivotally connected with its end with the articulated arm via attachment point, and the piston hydraulic cylinder is pivotally connected with one end in the attachment point with the ends (5a, 6a) of the first and second lever element, while the belonging piston cylinder is pivotally connected with its second end with the lift arm via attachment point and the articulated arm is centrally attached to the lift arm, and wherein the length of the first lever element is longer than the length of the second lever element, and the attachment point which connects both lever elements (5, 6) with the piston hydraulic cylinder is located below the attachment point of the end of the second lever element with the articulated arm, while the crane is in the operating position, and the attachment point is located above the attachment point while the crane is in the folded position, and wherein the distance (x) between the attachment point of the lift arm with the articulated arm and the attachment point of the end of the hydraulic piston cylinder with the lift arm exceeds the distance (y) between the attachment point of the lift arm with the articulated arm and the attachment point of the end of the second lever element with the articulated arm, and the distance (z) between the attachment point of the lift arm with the articulated arm and the attachment point of the end of the first lever element with the lift arm is smaller than the distance (x) and smaller than the distance (y). each piston hydraulic cylinder includes a belonging set of levers, and the two sets of levers are connected with each other by a linking element via pivotal attachment which connects both lever elements with the piston hydraulic cylinder, and wherein each of said sets of levers consists of a first lever element that has two ends (5a, 5b) and a second lever element that has two ends (6a, 6b), and the first lever element and the second lever element are pivotally connected with each other through the first ends and via attachment point and the first lever element is pivotally connected with its end with the lift arm via attachment point and the second lever element is pivotally connected with its end with the articulated arm via attachment point, and the piston hydraulic cylinder is pivotally connected with one end in the attachment point with the ends (5a, 6a) of the first and second lever element, while the belonging piston cylinder is pivotally connected with its second end with the lift arm via attachment point and the articulated arm is centrally attached to the lift arm, and wherein the length of the first lever element is longer than the length of the second lever element, and the attachment point which connects both lever elements (5, 6) with the piston hydraulic cylinder is located below the attachment point of the end of the second lever element with the articulated arm, while the crane is in the operating position, and the attachment point is located above the attachment point while the crane is in the folded position, and wherein the distance (x) between the attachment point of the lift arm with the articulated arm and the attachment point of the end of the hydraulic piston cylinder with the lift arm exceeds the distance (y) between the attachment point of the lift arm with the articulated arm and the attachment point of the end of the second lever element with the articulated arm, and the distance (z) between the attachment point of the lift arm with the articulated arm and the attachment point of the end of the first lever element with the lift arm is smaller than the distance (x) and smaller than the distance (y).