In a method for forming microlenses, an etching process is performed by using a processing gas on an object to be processed provided with a substrate, a lens material layer formed on the substrate and a mask layer of a lens shape formed on the lens material layer to etch the lens material layer and the mask layer, so that the lens shape of the mask layer is transcribed to the lens material layer. The processing gas is a gaseous mixture of a gas containing fluorine atoms but no carbon atoms and a fluorocarbon-based gas having a ratio of the number of carbon atoms to the number of fluorine atoms which is greater than or equal to 0.5, the gaseous mixture having no oxygen gas.