Apparatus to apply a corrosion protecting layer, being initially in liquid form, to the surfaces of a ventilation chamber of a braking band of a disk brake disc, wherein - said braking band comprises two annular plates (6, 7) having the same predefined rotation axis (X-X); - said plates (6, 7) facing each other, thus defining said ventilation chamber therebetween, said chamber comprising ventilation chamber surfaces and an inner annular air inlet edge opening facing the rotation axis (X-X) and an outer annular air outlet edge opening opposite the air inlet edge opening in the transversal or radial direction relative to the rotation axis (X-X); - said plates (6, 7) being connected to each other by a plurality of connection members defining ventilation ducts arranged inside said ventilation chamber and defining said ventilation chamber surface; said apparatus comprising: - supporting means of the braking band for rotating the latter around said axis (X-X); - rotating means of said supporting means; - corrosion protecting liquid-directing means through said air outlet edge opening or said air inlet edge opening towards said ventilation chamber; - suction-applying means; characterized in that - said corrosion protecting liquid-directing means in the ventilation chamber comprise means for applying a preset pressure to said liquid before it flows out of said liquid-directing means in the ventilation chamber, and outflowing means of said pressurized liquid comprising a liquid outflow opening that is capable to cause a separation of said liquid particles, thus resulting in the atomization thereof; - said suction-applying means are arranged so as to act through the same edge opening (9 or 8) which said means act on in order to direct the corrosion protecting liquid to the ventilation chamber. - said braking band comprises two annular plates (6, 7) having the same predefined rotation axis (X-X); - said plates (6, 7) facing each other, thus defining said ventilation chamber therebetween, said chamber comprising ventilation chamber surfaces and an inner annular air inlet edge opening facing the rotation axis (X-X) and an outer annular air outlet edge opening opposite the air inlet edge opening in the transversal or radial direction relative to the rotation axis (X-X); - said plates (6, 7) being connected to each other by a plurality of connection members defining ventilation ducts arranged inside said ventilation chamber and defining said ventilation chamber surface; - supporting means of the braking band for rotating the latter around said axis (X-X); - rotating means of said supporting means; - corrosion protecting liquid-directing means through said air outlet edge opening or said air inlet edge opening towards said ventilation chamber; - suction-applying means; - said corrosion protecting liquid-directing means in the ventilation chamber comprise means for applying a preset pressure to said liquid before it flows out of said liquid-directing means in the ventilation chamber, and outflowing means of said pressurized liquid comprising a liquid outflow opening that is capable to cause a separation of said liquid particles, thus resulting in the atomization thereof; - said suction-applying means are arranged so as to act through the same edge opening (9 or 8) which said means act on in order to direct the corrosion protecting liquid to the ventilation chamber.