A motorized tool (2) for agricultural use, particularly of the energy- saving type, comprising at least one movable part (3) adapted to engage objects (7a) to be processed and means for varying the working speed of the movable part (3), and detection means (6) arranged at the inlet of the work area of the movable part (3) and adapted to detect objects (7a, 7b) entering the work area and functionally associated with the variator means so as to vary automatically the working speed of the movable part (3) between a working speed value equal to zero and a maximum speed value in relation to the presence and/or consistency of the objects (7a, 7b).
