Abstract: A titanium stripping solution comprises an aqueous solution of pH 5 or lower containing a fluorine compound and a metal ion having a reducing power, which enables etching of titanium at a high etching rate by the fluorine compound with exhibiting an effect of suppressing corrosion of other metal(s).

Abstract: There are provided a treatment solution for reducing a copper oxide formed on the surface of copper to copper, wherein dimethylamine borane is contained in an amount of 0.3 to 2.0 g/L and the relationship y≧0.232x−0.185 holds between the concentration y (g/L) of dimethylamine borane and an area x (dm2/L) to be treated per unit solution amount, and a treatment method for reducing a copper oxide formed on the surface of a copper material to copper by dipping the copper material in the treatment solution as described above, wherein the addition of dimethylamine borane to water is carried out within 10 minutes before the dipping of the copper material or after the dipping of the copper material.