PURPOSE: To enable the control of atmosphere and to prevent the surface oxidation of a conductive roll and the spark between the conductive roll and a metal sheet by surrounding only the long-torsoed part of the conductive roll with a furnace shell in a heating device for conducting the current to the metal sheet through the conductive roll.

CONSTITUTION: Only the long-torsoed part 3 of the conductive roll 2 is surrounded with the furnace shell 5, and a rolling reduction device 12 and roll stands 13 provided with collecting brushes 11 are arranged at the outside of the furnace. As the metal sheet 1 as a metarial to be heated and the long- torsoed part 3 of the conductive roll 2 are in the furnace shell 5, it is easy to execute the atmospheric control for the purpose of preventing from the surface oxidation. The rolling reduction of the metal sheet 1 is executed by applying the force to bearings 9 by the rolling reduction device 12, and as these devices are arranged at the outside of the furnace, influence of heating is not affected and the stable rolling reduction can be executed. Further, since the collecting brushes 11 are arranged to the side par of the roll stand 13, even if the wearing powder is produced, its sticking on the surface of the barrel part 3 of the conductive roll from the furnace shell 5 can be prevented.