To eliminate metallic contamination from the surface of electronic material under easy conditions and efficiently, by bringing the washed object into contact with acid-dissolved wash water and then with oxidant-dissolved wash water.

A washed object is brought into contact with acid-dissolved wash water and then with oxidant-dissolved wash water. The wash water is adjusted using a reagent of high purity and superpure water. As for acid, hydrochloric acid, sulfuric acid, or nitric acid is preferably used. And, it is preferred that the pH of the acid-dissolved wash water is 4 or below, notably, 2 or below. As for the oxidant, ozone, hydrogen peroxide, sodium hypochlorite, sodium chlorite, sodium chlorate, or the like is preferably used. Among them, ozone is especially preferred because it exhibits noticeable effect even in extremely low density. The density of ozone in the wash water is preferably 0.1 mg/liter or above, notably, 1 mg/liter or above.