A lifting jack has a lifting mechanism (13) housed in a casing (12). The lifting mechanism (31) consist of a threaded rod (10), a worm-wheel (11) provided with a central threaded opening (43) engaged with the threaded rod (10) and a motor driven worm screw (44) engaged with the worm-wheel (11). The worm-wheel (11) is rotatably mounted by means of bearings in the casing (12). The threaded rod (10) is furnished with a groove (14) which engages with a protrusion (54) to avoid its rotation of the threaded rod. A foot (15) is pivotally mounted on an end of the threaded rod (10).
