The present invention relates to an agricultural machine comprising an improved device for controlling a shield. Said agricultural machine has at least one working tool (2) which can be driven by a drive means (3) which can have a variable drive speed, at least one movable shield means (4) which can be moved at least between operational and non-operational positions, and a device for moving said at least one shield means (4), comprising at least one adjusting actuator (7) and a device for locking the shield means. The machine (1) is characterised in that the movement device has 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 for preventing said 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 means (3) or on the working speed of the at least one tool (2) in question.
