A haymaking machine, or a windrower, including a support structure including a main beam on which is articulated at least one lateral arm supporting at least one windrowing rotor. The rotor is connected to a support device forming an interface with a support mounted on the lateral arm. The support device makes it possible for the rotor to displace to follow movements of the terrain when the machine is in operation and is in a work position. The support device includes an adjustment system allowing to limit movements of the rotor in the work position and to block movements of the rotor in other positions, and the adjustment system allowing to limit the movements of the rotor includes a control including a hydraulic jack.