A support device, to be hooked up to a hitching device of a tractor: the support device includes a chassis 10 as a machine-welded metal structure which is fixed at 20 to the hitching device, and a platform extending cantilevered relative to the fixing device, the platform has an upper side 16 equipped at 160 to pre-position and center a box 40 to be supported on the platform, and a lower side 19 including at least one accommodating housing 191, 192 for cooperating with a corresponding protuberance 51, 52 of an add-on weight 50, intended to be supported under the platform to provide an anchoring in the shape of a “dovetail” type connection extending in the longitudinal direction substantially parallel to the direction of travel of the tractor.