Abstract: A sliding electric contact device for welding head for roller welding machines, having a bimetallic plate adapted to be fixed to a shaft of a welding head, having a protection base composed of a first metal, defining a first face destined to abut against an end surface of the shaft, and a sliding disk composed of a second metal softer than the first metal, defining a second sliding electric contact face; a composite current-carrying block, having a plait of electrical wires, an internal support made of metal, pushed against the sliding disk for realizing with the sliding disk a sliding electric contact, first means adapted to fix firmly a central portion of the plait to the inner support, second current-carrying means adapted to fix firmly a peripheral portion of the plait to current terminals of a stator of the welding head. A welding head having the sliding electric contact device and a related roller welding machine are also disclosed.