In addition, when ascorbic acid or a thioglycollic acid-based compound is added to the cleaning liquid, it is preferable that the concentration of the reducing agent such as ascorbic acid or a thioglycolic acid-based compound is not less than 0.001 mol/L and not more than 0.06 mol/L (preferably not less than 0.2 wt % and not more than 0.5 wt %.