Abstract: A ring rolling mill comprising a driven working roll, a rotary mandrel serving as a counter-roll, and a containment roller carried by a pivoted arm and able to engage laterally the ring being rolled, further includes a tracer roller carried by a respective pivoted arm. The assembly formed by the tracer roller and its respective arm is a mirror image of the assembly formed by the containment roller and its respective arm across the vertical plane identified by the axes of rotation of the working roll and of the mandrel which are both vertically orientated. Means for detecting the angular position of the tracer arm and of the containment arm are connected to an electrical control circuit of an hydraulic servo valve for regulation and locking of the angular movement of the containment arm so as to maintain the containment roller in a symmetrical position with respect to the tracer roller across the vertical plane.