To equalize partial pressure of an organic substance inside a vacuum vessel containing an electron emitting element, effectively remove gas adsorbed to respective parts in the vacuum vessel in an activating process, reduce the occurrence of failure in the vacuum vessel after vacuum sealing in a process of manufacturing an image forming device, and improve a manufacturing yield of the image forming device.

In manufacturing an electron emitting element, a conductive thin film 4 electrically connected to a pair of element electrodes 2, 3 is provided, an organic film 6 mainly composed of the whole aromatic polyimide is arranged on the conductive thin film 4, and voltage is impressed on a pair of electrodes so as to be carbonized. This polyimide is laminated in a multilayer shape.