An optical element comprising at least a plurality of pixels formed on a substrate and partition walls arranged respectively between adjacent pixels is manufactured by a method comprising steps of forming partition walls of a resin composition on a substrate, performing a dry etching process by irradiating the substrate carrying the partition walls formed thereon with plasma in an atmosphere containing gas selected from oxygen, argon and helium, performing a plasma treatment process by irradiating the substrate subjected to the dry etching process with plasma in an atmosphere containing at least fluorine atoms, and forming pixels by applying ink to the areas surrounded partition walls by means of an ink-jet system.