A sealing device is arranged around a rod electrode extending vertically through an aperture made in the ceiling of an arc furnace and being vertically movable inside the furnace to prevent the access of gases from the furnace through the aperture to the atmosphere, and on the other hand to prevent air from flowing from the atmosphere into the furnace. The sealing device comprises a gas distribution chamber provided with an inlet channel for feeding essentially passive gas, such as nitrogen or air, into the gas distribution chamber. The sealing device also includes a slit nozzle encasing the electrode, through which nozzle a gas jet is arranged to be discharged from the gas distribution chamber towards the electrode in a direction that is at an angle with respect to the horizontal plane and has a slightly upwards inclined orientation, and that is, with respect to the furnace interior, pointed outwardly, so that the sealing is carried out owing to the effect of the created stagnation pressure.
