A surface conditioner contains zinc phosphate particles of D50 of 3 μm or less and has a pH of 3 to 12, and also contains at least one of (1) carboxylate group-containing copolymers obtained by copolymerizing a monomer composition containing at least one species selected from acrylic acid, maleic acid, maleic anhydride, itaconic acid and itaconic anhydride in an amount less than 50% by weight and at least one species selected from the group consisting of a sulfonic acid monomer, styrene, olefin monomers, amino group-containing monomers and certain polyoxyalkylene derivatives, (2) certain polyamino acids, and (3) certain phosphate esters.