One of a setting dissolved oxygen concentration and a setting atmosphere oxygen concentration is determined based on a required etching amount. Thereafter, based on the required etching amount and the one of the determined setting dissolved oxygen concentration and setting atmosphere oxygen concentration, the other of the setting dissolved oxygen concentration and the setting atmosphere oxygen concentration is determined. A low oxygen gas whose oxygen concentration is equal or approached to the determined setting atmosphere oxygen concentration flows into a chamber that houses a substrate. Furthermore, an etching liquid whose dissolved oxygen is reduced such that its dissolved oxygen concentration is equal or approached to the determined setting dissolved oxygen concentration is supplied to the entire region of the upper surface of the substrate held horizontally.