Haymaking machine, more particularly a windrower for plants lying on the ground. The haymaking machine has a support structure including a main beam (1) on which is articulated a lateral arm (2) supporting a windrowing rotor (5). The rotor (5) is connected to a support device (12) forming an interface with a support (9) mounted on the the lateral arm (2). The support device (12) allows displacements for the rotor (5) so as to follow the movements of the terrain when the machine is in operation and is in work position. The support device (12) includes an adjustment system allowing to limit the movements of the rotor relative to the support (9) about a first axis and a second axis in the work position and to block them in other positions. The adjustment system allowing to limit the movements of the rotor includes on the one hand a control means including at least one hydraulic jack, and on the other hand a connecting device movable by the at least one hydraulic jack (13).
