A jack, defining a portable accessory for replacing a motor vehicle wheel, is adapted to be placed on the ground and has a scissors-like pantograph provided with a first and a second arm hinged to each other; the first and second arms have respective lower end portions, which can be moved close or away by actuating a screw/nut-screw device; the second arm is shorter than said first arm and is provided with an upper end portion hinged to an intermediate portion of the first arm; the jack further has a supporting member, which is supported only by an upper end of the first arm and can rotate about an axis.