The substrate processing apparatus includes: a nozzle having a spout and adapted to spout SPM from the spout toward a substrate; a mixing portion communicating with the spout; a sulfuric acid-containing liquid supply device which recovers liquid supplied to and expelled from the substrate held by a substrate holding unit, prepares a sulfuric acid-containing liquid from the recovered liquid, and supplies the prepared sulfuric acid-containing liquid to the mixing portion; and a control device. The control device performs: a sulfuric acid-containing liquid preparing step of recovering SPM supplied to and expelled from the substrate and preparing the sulfuric acid-containing liquid; and an SPM spouting step of supplying the prepared sulfuric acid-containing liquid and hydrogen peroxide water to the mixing portion, mixing the sulfuric acid-containing liquid and hydrogen peroxide water together in the mixing portion to prepare SPM, and spouting the prepared SPM from the spout.