A fine treatment agent according to the present invention is a fine treatment agent for the fine treatment of a multilayer film, including a tungsten film and a silicon oxide film comprising at least one from among hydrogen fluoride, nitric acid, ammonium fluoride and ammonium chloride. Thus, a fine treatment agent which makes fine treatment on a multilayer film, including a tungsten film and a silicon oxide film, possible by controlling the etching rate and a fine treatment method using the same can be provided.