An apparatus which selectively etches a first region with respect to a second region made of a material different from that of the first region. The apparatus is controlled to perform a first step for generating, in a processing container housing a workpiece to be treated, a plasma of a treatment gas from a gas supply including a fluorocarbon gas, an oxygen-containing gas, and an inert gas, and forming a deposit including fluorocarbon on the object to be treated, and a second step for etching the first region with radicals of the fluorocarbon included in the deposit. The apparatus is also controlled to perform the first step and the second step repeatedly.