A mower with a variable cutting width with respect to the movement direction comprising: - cutting rotors (71, 72, 73, 74) of a type having an axis of rotation that is vertical with respect to the ground surface; - transmission means for transmitting the motion which comprise shafts (81, 82, 83, 84), each coupled to a respective cutting rotor (71, 72, 73, 74) so as to set the cutting rotor (71, 72, 73, 74) in rotation about a respective rotation axis; - a cutting rotors (71, 72, 73, 74) cover assembly comprising a first part which has a first hole housing a first shaft coupled to a first cutting rotor and rotationally connected to the first part and a second part which has a second hole housing a second shaft coupled to a second cutting rotor and rotationally connected to the second part; wherein the second part and the first part are mutually movable according to a first direction transversal to the movement direction of the mower between a first position and a second position in which the distance between the second shaft and the first shaft is greater than in the first position so as to vary the cutting width, the mower being characterised in that: - the displacement in the first direction of the second part with respect to the first part between the first position and the second position is greater than a first distance in the first direction between the edges of the first hole and the second hole in the first position; - the second part has a recess which faces towards the first shaft so as to accommodate the first shaft at least in the first position; - the cutting rotors (71, 72, 73, 74) cover assembly comprises a closing part which comprises a first seat which houses the first shaft, a second seat which houses the second shaft and, between the first and second shaft (81, 82), a solid part; - the first seat extends so that in the first position the closing part is movable with respect to the first shaft by a first displacement in the first direction in a first sense, the second seat extends so that in the first position the closing part is movable with respect to the second shaft by a second displacement in the first direction in a second sense, opposite the first sense and the scalar sum of the first displacement and of the second displacement is greater than the first distance so as to allow a displacement between the first part and the second part that is greater than the first distance; - the solid part extends in the first direction so as to be at the part of the recess that is not covered by the first part. - cutting rotors (71, 72, 73, 74) of a type having an axis of rotation that is vertical with respect to the ground surface; - transmission means for transmitting the motion which comprise shafts (81, 82, 83, 84), each coupled to a respective cutting rotor (71, 72, 73, 74) so as to set the cutting rotor (71, 72, 73, 74) in rotation about a respective rotation axis; - a cutting rotors (71, 72, 73, 74) cover assembly comprising a first part which has a first hole housing a first shaft coupled to a first cutting rotor and rotationally connected to the first part and a second part which has a second hole housing a second shaft coupled to a second cutting rotor and rotationally connected to the second part; - the displacement in the first direction of the second part with respect to the first part between the first position and the second position is greater than a first distance in the first direction between the edges of the first hole and the second hole in the first position; - the second part has a recess which faces towards the first shaft so as to accommodate the first shaft at least in the first position; - the cutting rotors (71, 72, 73, 74) cover assembly comprises a closing part which comprises a first seat which houses the first shaft, a second seat which houses the second shaft and, between the first and second shaft (81, 82), a solid part; - the first seat extends so that in the first position the closing part is movable with respect to the first shaft by a first displacement in the first direction in a first sense, the second seat extends so that in the first position the closing part is movable with respect to the second shaft by a second displacement in the first direction in a second sense, opposite the first sense and the scalar sum of the first displacement and of the second displacement is greater than the first distance so as to allow a displacement between the first part and the second part that is greater than the first distance; - the solid part extends in the first direction so as to be at the part of the recess that is not covered by the first part.