An etching apparatus includes a reaction chamber having an internal space, a fixing chuck disposed in the reaction chamber, an electrostatic chuck disposed on the fixing chuck and on which a wafer is placed, a focus ring surrounding the electrostatic chuck, and a sensor device configured to be transferred into or out of the reaction chamber and placed on the electrostatic chuck. The sensor device includes a body having a plate shape, and a sensor disposed on an upper surface of the body which senses whether the focus ring is worn.