The present invention provides a method of manufacturing an electron source which exhibits improved uniformity of electron emitting devices and electron emission properties, and a method of manufacturing an image forming apparatus which exhibits an excellent display quality for a long time. An electron source having a plurality of electron emitting devices is manufactured by disposing a plurality of units, each comprising a pair of electrodes and a polymer film for connecting the electrodes, on a substrate, disposing a plurality of wirings for connection to the pair of electrodes of the plurality of each unit, and decreasing the resistances of all polymer films respectively of the units. A next step includes applying a voltage to films formed by decreasing the resistances of the polymer films, through the wirings, to form a gap in each of the films formed by decreasing the resistance of the polymer films.