PURPOSE: To reduce the thermal load of a rolling roll by effectively heating the ring material which is rolled between upper and lower rolling rolls.

CONSTITUTION: A guide roll 9 which is brought into contact with a ring material 3 to be rolled is arranged on the upstream side of upper and lower rolling rolls 1, 2. A conducting line 5 is provided between the guide roll 9 and the power source 4. A conducting line 6 is provided between the upper rolling roll 1 and the power source 4. A conducting circuit 11A is constituted where the current from the power source 4 runs through the conducting line 5, the guide roll 9, the ring material 3, the upper rolling roll 1, and the conducting line 6. The part of the ring material 3 which is located between the upper and lower rolling rolls 1, 2 and the guide roll 9 is conducted and heated by the conducting circuit 11A.