Pivotable hydraulic telescopic supporting leg for a mobile land transporting or working machine, in particular for a truck hydraulic crane, wherein such supporting leg consists of a tubular housing, which is blinded on its one side, where at least one hydraulic conduit of a hydraulic circuit is connected thereto, while on its opened end portion a telescopic arm is inserted there-into, which is by means of a hydraulic media available within said hydraulic circuit displaceable to and fro along a geometric axis of the supporting leg, wherein on the blinded end portion (111") of said housing a tubular bearing casing is available, the central axis of which extends perpendicularly with respect to said geometric axis of the supporting leg, and wherein said supporting leg is pivotally connected to a telescopic beam, by which each mobile land transporting or working machine is mounted on a chassis of each disposable land vehicle and which consists of a tubular casing, which is open on both terminal end portions and into which on each end portion (31', 31") a telescopic arm (32', 32") is inserted, which is movable to and fro by means of the hydraulic media available within said hydraulic circuit and is on its free end portion, which protrudes outside from said casing, furnished with a hinge, on which a supporting leg is attached by means of its tubular bearing casing and pivotally around the geometric axis, which extends perpendicularly with respect to said longitudinal axis of the supporting leg, and said leg can be fixed in each desired position, characterized in that said supporting leg comprises a ring-shaped hydraulic interface with flat front surfaces (21, 22) and uninterrupted external circumferential surface, wherein said hydraulic interlace is arranged adjacent to said bearing casing of the supporting leg and is analogously like said casing of the supporting leg itself pivotally placed on the hinge of each corresponding telescopic arm (32', 32") of the beam, wherein said interface is allowed to be pivoted at each desired angle around said axis of the hinge and relatively to said beam and is by means of a suitable sealing assembly in the area of both flat front surfaces (21, 22) hydraulically sealed both against said bearing case of the supporting leg as well as against to each belonging hinge on the telescopic arm (32', 32") of the beam, and wherein said hydraulic interface is on its inner cylindrical surface furnished with at least one circumferentially extending and uninterrupted groove, which is arranged at sufficient distance apart of said front surfaces (21, 22) and is adapted to receive a hydraulic media from the hydraulic circuit, and said hydraulic interface is moreover furnished with at least one hydraulic connector (241, 242), which is arranged in the area of said groove and is on the external surface of said interface connected with a corresponding hydraulic conduit, which is arranged on the supporting leg and belongs to said electric circuit, wherein said hinge is furnished with a transversal passage, through which the hydraulic media is able to flow from the hydraulic circuit towards the area of said groove in said hydraulic interface, or in opposite direction.