A welding head for welding the extremities of two sections of rail and comprises two half-heads (10) aligned and sliding with regard to one another in a longitudinal direction. Each half-head comprises grip mechanism (12, 13) for grasping a respective section of rail and two electrodes (16) suitable for contact with respective sections of rail in order to carry out a flash butt weld. The head also comprises traction actuator mechanisms (20) which extend in a longitudinal direction and are connected to the two half-heads (10) to shift the two half-heads in a longitudinal direction one towards the other, the traction actuator mechanism (20) having a stroke suitable for allowing, during a cycle of welding two sections of rail, simultaneous regulation of rail tensions.