A safety device (1) is described based on the presence of an operator on a seat (2), particularly for tractor mower, comprising a switch (3) for the re-establishment of the safety conditions in case of the absence of the operator from the seat (2), and operating means (4) of the switch (3) in association with the presence or not of the operator on the seat (2). Said device envisages a fixed inferior support (6) of the switch (3) integral with the frame (7) of the tractor, a mobile superior support (8) of an operating means (4) of the switch (3) vertically slidable along guiding pins (51) and associated with the lowering of the seat (2) in the presence of the operator by means of shock absorbers (9) integral with said mobile support (8), springs (11) interposed between the fixed support (6) and the mobile support (8) and slidably embracing the vertical guiding pins (51). The fixed support (6) and the mobile support (8) are in relation of reciprocal reversible insertion between them in case of the presence of the operator on the seat (2), The switch (3), the operating means (4) and the springs (11) are enclosed between the fixed support (6) and the mobile support (8). ( Fig.1 ).
