An apparatus and a method for the treatment of a flat steel product, taking place in throughput. The apparatus includes an indirectly heated annealing furnace chamber, a conveyor device for continuously conveying the flat steel product over a conveyor path leading from an entry to an exit of the annealing furnace chamber, and nozzle arrangements for feeding atmosphere gas, which is reactive in relation to the flat steel product, into the annealing furnace chamber. A controlled treatment of the flat steel product includes a first nozzle arrangement, from which a gas jet induces a first gas flow towards the entry of the annealing furnace chamber and sweeping over the surface of flat steel product to be treated. A second nozzle arrangement includes a gas jet which induces a second gas flow directed towards the exit of the annealing furnace chamber and sweeping over the surface of flat steel product.