Castor for assisting with the movement by rolling of a piece of furniture (Mbl) when it is capable of being located in an environment, where a gravitational force is present, and that it is capable of resting on a floor via the castor, the latter comprising at least one wheel casing and a generally cylindrically-shaped revolving pivot defining an axis of rotation, said pivot being mounted, by a first end, engaged with said wheel casing in an opening made in it, said opening having a shape, substantially complementary to that of said pivot such that the latter is capable of pivoting there, the axis of said opening being coaxial with said axis of rotation, said pivot being capable of being linked to the furniture by its second end, the castor comprising • an annular housing made in the wall of said opening, said housing comprising: - a first wall rotating all around the wall of said opening and being defined in a plane substantially orthogonal to said axis of rotation, the castor being characterised by the fact that it comprises: - a second wall defining a section inclined with respect to said axis of rotation, said inclined section being rotated towards the first wall and having a given slope Pp, this second wall forming an open loop, the free ends (122, 123) of which define a window, the length of which, defined in a plane perpendicular to said axis of rotation, has a value Ld, • a lug made projecting over and integral with the outer wall of the first end of said pivot, this lug having a length, taken in a direction perpendicular to said axis of rotation, of value at most equal to the value Ld, • said lug being made on said pivot such that, when said furniture (Mbl) rests on a floor, said lug rests on the first wall of the housing and that, when said furniture is distant from the floor, the casing thus undergoing a relative movement with respect to the pivot, said lug moves away from the first wall and, during this relative movement, is housed in said window after having optionally slid over the inclined section of the second wall of the housing, and due to this, driven the rotation of the casing with respect to the pivot. • an annular housing made in the wall of said opening, said housing comprising: - a first wall rotating all around the wall of said opening and being defined in a plane substantially orthogonal to said axis of rotation, the castor being characterised by the fact that it comprises: - a second wall defining a section inclined with respect to said axis of rotation, said inclined section being rotated towards the first wall and having a given slope Pp, this second wall forming an open loop, the free ends (122, 123) of which define a window, the length of which, defined in a plane perpendicular to said axis of rotation, has a value Ld, - a first wall rotating all around the wall of said opening and being defined in a plane substantially orthogonal to said axis of rotation, the castor being characterised by the fact that it comprises: - a second wall defining a section inclined with respect to said axis of rotation, said inclined section being rotated towards the first wall and having a given slope Pp, this second wall forming an open loop, the free ends (122, 123) of which define a window, the length of which, defined in a plane perpendicular to said axis of rotation, has a value Ld, • a lug made projecting over and integral with the outer wall of the first end of said pivot, this lug having a length, taken in a direction perpendicular to said axis of rotation, of value at most equal to the value Ld, • said lug being made on said pivot such that, when said furniture (Mbl) rests on a floor, said lug rests on the first wall of the housing and that, when said furniture is distant from the floor, the casing thus undergoing a relative movement with respect to the pivot, said lug moves away from the first wall and, during this relative movement, is housed in said window after having optionally slid over the inclined section of the second wall of the housing, and due to this, driven the rotation of the casing with respect to the pivot.