An aqueous solution (20) of an alkali hydroxide is stored and held in a tank (1). An electrode (5) is disposed in the tank (1), and a member (11) coated with a Ti-derived film is disposed in the tank (1) so as to be surrounded with the electrode (5). In this state, a power source (6) applies a negative potential to the electrode (5) and a positive potential to the member (11) to flow electricity between the electrode (5) and the member (11) immersed in the aqueous solution (20). Thus, the Ti-derived film coated on the surface of the member (11) is chemically removed by the aqueous solution (20).