The invention relates to a support device for a railing arranged on a surface, characterised in comprising a base(20) with a transverse section essentially in the shape of an inverse T, said base comprising a central wing (21) finished with a transverse wing (22) at the bottom thereof, the lower face of said transverse wing (22) serving as the mounting surface, the centre web having two cavities, a first cavity (28) to accommodate the bottom end of a post (29) and a second cavity (30) to accommodate one end of a crosspiece (31), wherein the base (20) is formed by the assembly of two part bases (36, 37), each comprising a central half wing and a transverse half wing in a joint plane essentially corresponding to the longitudinal plane of symmetry of the base (20); each half base (36, 37) having two concave indentations (38, 39) at the level of said joint plane corresponding to said cavities (28, 30) and the depth of which, measured perpendicularly to the joint plane is less than half the width of the post (29) and the crosspiece(31), measured at a corresponding point. The fixing for the two half bases (36, 37) to each other and to the post (29) and crosspiece being carried out by screwing (31).