The device comprises a frame (10) bearing an articulated arm (2) to which is coupled a machine (3) for cutting plants. The articulated arm (2) is formed of at least one lower segment (21), the lower end of which is mounted to be mobile in rotation in a point of articulation (12) of the frame, a lower piston-cylinder unit (41) being arranged between said frame (10) and said lower segment (21) in order to adjust the angle A formed by said lower segment (21) with the horizontal. According to the invention, the lower piston-cylinder unit (41) is a single-action piston-cylinder unit for the work of cutting grass or low hedges, and is a double-action piston-cylinder unit when working at a height for which the angle A is greater than a given value.
