There is disclosed a self-propelled lawnmower wherein the wheels are mounted on a fixed frames surrounded, at least on its two lateral faces, by fixed protective skirts which extend practically to ground level. A cutting assembly is mounted on a secondary chassis which can be displaced with respect to the fixed chassis supporting the wheels. A linkage between the two chassis is provided by tilting levers that pivot on the fixed chassis and allow the secondary chassis to be vertically displaced thereon. Movement is transmitted to the drive wheels by a drive gear that engages a ring gear arranged inside each drive wheel, the drive gears being displaceable along the pitch circles of the ring gears when the secondary chassis is displaced.