A method for forming micro lenses includes the step of performing an etching treatment to an object to be processed, which includes a lens material layer and a mask layer having lens shapes and formed on the lens material layer, using an etching gas including SF6 gas and CHF3 gas, an etching gas including SF6 gas and CO gas, an etching gas including a gas having therein carbon and fluorine and CO gas, or an etching gas including two or more kinds of gases from a first gas having therein carbon and fluorine and a second gas having therein carbon and fluorine, to etch the lens material layer and the mask layer and transfer the lens shapes of the mask layer to the lens material layer, thereby forming the micro lenses.