To provide a forming method of a black oxide film capable of preventing deterioration in tension of a color selection electrode structure to which the tension in the slit extension direction is applied.

The forming method of the black oxide contains a heating process for heating the color selection electrode structure using an aperture grille to 400°C in the atmosphere of mixed gas obtained by mixing 8-12 volume% air to exothermic converted gas having the specified composition; a temperature keeping process for heating the color selection electrode structure of 400°C to 460°C in the atmosphere of only the exothermic converted gas and then keeping at 460°C for about 15 minutes; and a cooling process for cooling the color selection electrode structure of 460°C to 200°C in the atmosphere of mixed gas obtained by mixing 5-15 volume% air to the exothermic converted gas.