A system for automatic positioning of a railway overhead line comprising: a mechanical arm (12); a first hooking device (31) that can be fixed to the end of the mechanical arm (12); a mast (40) for positioning an overhead line; a second fixed hooking device (41), which is fixed to the mast (40) and can be fixed to the first hooking device (31); the mast (40) comprising at least one horizontal arm (52), set on which is a set of rollers (53), with roller head, for correct positioning of an overhead line.