A method of etching an etching target layer containing polycrystalline silicon includes preparing a target object including the etching target layer and a mask formed on the etching target layer; and etching the etching target layer with the mask. Further, the mask includes a first mask portion formed of polycrystalline silicon and a second mask portion interposed between the first mask portion and the etching target layer and formed of silicon oxide. Furthermore, in the etching of the etching target layer, a first gas for etching the etching target layer, a second gas for removing a deposit adhering to the mask, and a third gas for protecting the first mask portion are supplied into a processing vessel in which the target object is accommodated, and plasma of these gases is generated within the processing vessel.