A first SPM, prepared by mixing sulfuric acid and hydrogen peroxide water at a first mixing ratio, is supplied to a substrate. A second SPM, prepared by mixing the sulfuric acid and the hydrogen peroxide water at a second mixing ratio greater than the first mixing ratio, is supplied to the substrate after the supply of the first SPM is stopped. The first SPM expelled from the substrate flows into a drain piping. The second SPM expelled from the substrate flows into a recovery piping. SPM is prepared by mixing the hydrogen peroxide water with sulfuric acid contained in the second SPM guided by the recovery piping.