An agricultural machine including at least one working tool which can be driven by a drive mechanism which can have a variable drive speed, at least one movable shield which can be moved at least between operational and non-operational positions, and a device for moving the at least one shield, including at least one adjusting actuator and a device for locking the shield. The movement device includes a circuit for controlling the actuator which includes the locking device, which circuit automatically converts a variable input quantity into a control quantity which can adopt a first control value used to prevent the adjusting actuator from being moved out of a first configuration, the input quantity being a value which is a function of or dependent on the drive speed of the drive mechanism or on the working speed of the at least one tool.
