A cutting device for lawn-mower comprises a support body (5) that can be associated at the bottom with a lawn-mower (1) a cutting blade (9) associated with said support body (5) and able to rotate for cutting said grass surface a first sensor (13) associated with the support body (5) and located in correspondence of the cutting blade (9) for detecting the presence of said grass surface, and a second sensor (14) associated with the support body (5) and located at a height intermediate between that of said support body (5) and said cutting blade (9) for detecting the presence of grass to be cut. A lawn-mower comprises said cutting device.
