An oxidation treatment method of the present invention includes the step of bringing a solution having an ozone concentration of 120 to 500 mg/L into contact with a substance to be treated made of a combustible substance, thereby subjecting the substance to be treated and the surface thereof to an oxidation treatment. An oxidation treatment apparatus of the present invention includes: a dissolving means that dissolves an oxygen-ozone mixed gas in a fluorine-based solvent to form mixed fluid; an undissolved gas removal means that removes an undissolved gas from the mixed fluid to form a solution; and an oxidation treatment means that brings the solution into contact with a substance to be treated made of a combustible substance, thereby subjecting the substance to be treated and the surface thereof to an oxidation treatment.