The present invention provides a resin composition comprising: a urethane resin and/or a resin as obtained by polymerizing a monomer component including an α,β-unsaturated carboxylic acid as an essential component; and a multivalent metal compound; which resin composition is excellent in the one-liquid stability and also in the coating-film appearance, coating-film adhesion, water-rubbing resistance, warm-water-whitening resistance, and blocking resistance. The resin composition, according to the present invention, comprises: the urethane resin and/or the resin as obtained by polymerizing the monomer component including the α,β-unsaturated carboxylic acid as an essential component; and the multivalent metal compound; with the resin composition being characterized by further comprising tartaric acid and/or its salt.