A mobile telescopic hydraulic crane, comprising a carrying platform, which is suitable for mounting the crane on each motor vehicle and is fitted with at least one pair of telescopic suitable legs for supporting the crane on the ground by manipulating with each and consequently for ensuring of a required carrying capacity and stability of said crane, furthermore, a column, which is in the area of its first terminal portion as a cantilever attached to said platform in such manner, that it can be rotated around the vertical axis, while on the free second terminal portion of said column a primary bearing arm of the crane is attached in the area of its first terminal portion, in such manner that it can be pivoted around the horizontal axis, wherein said primary arm is supported on said column and can be pivoted around said horizontal geometric axis by means of a hydraulic cylinder, which is on the one hand pivotally attached to said column, and is on the other hand attached to said primary arm, wherein on the second terminal portion of said primary arm, a telescopically conceived secondary bearing arm is attached with its first terminal portion in such manner, that it can be pivoted around the horizontal geometric axis, wherein said secondary bearing arm is on its second terminal portion furnished with an attachment point for mounting a grabber or another suitable assembly for manipulating with each load, wherein said telescopic secondary arm is supported on the primary arm and can be pivoted around said horizontal geometric axis by means of a hydraulic cylinder, which is on one hand either directly or indirectly via a suitable transmission mechanism pivotally connected to the primary arm and is on the other hand, again either directly or indirectly via a suitable transmission mechanism, connected to the secondary arm, wherein said secondary arm comprises at least two tubular bearing sections (44, 45), which are inserted within each other, so that said tubular bearing sections (44, 45) are by means of a suitable driving means moveable relative to each other in their axial direction in such manner, that the external tubular bearing section is intended for establishing a connection with the primary arm and attachment to a hydraulic cylinder, while the internal tubular bearing section within the external tubular bearing section is on its free end portion furnished with said attachment point for mounting a grabber, wherein on the one hand on the free terminal portion of the external tubular bearing section of the telescopic secondary arm at least one hydraulic connector is foreseen, which enables the hydraulic medium to flow from each available hydraulic aggregate, and on the other hand also on the free terminal portion of the internal tubular bearing section of the telescopic secondary arm at least one hydraulic connector is foreseen, which enables the hydraulic medium to flow towards said grabber and/or towards its corresponding hydraulic rotational unit, wherein said hydraulic connectors (431, 432) are connectable with each other by means of a flexible hydraulic pipe, which is connected which each of said hydraulic connectors (431, 432) in a hydraulically sealed manner, however in a detachable manner and by maintaining the ability of being disconnected and reconnected when required, and wherein said flexible hydraulic pipe extends along the interior of said telescopic secondary arm, namely between the hydraulic connector on the free terminal portion of the external tubular bearing section and the hydraulic connector on the free terminal portion of the internal tubular bearing section, and is in the area of transition from the external tubular bearing section into the internal tubular bearing section relatively sharply bended and guided thereby via a guiding reel, characterized in that at least one service opening (48, 48') is provided in the area of said telescopically conceived secondary arm, namely on its free terminal portion and at a suitable distance apart from the free terminal portion of said external tubular bearing section in the area of arrangement of said at least one hydraulic connector for connecting of said flexible hydraulic pipe, which is on the other hand connectable with each belonging hydraulic connector on the free terminal portion of the internal tubular bearing section, wherein said service opening (48, 48') has a suitable shape and dimensions, which are adjusted and sufficiently extensive to allow access there-through from the outside of the telescopic arm to each suitable hand tool, which is required either for establishing or disassembling of said hydraulically sealed connection between said flexible hydraulic pipe and each corresponding hydraulic connector within said telescopic arm.