PROBLEM TO BE SOLVED: To provide an ambient-temperature-curable one-pack type aqueous paint composition capable of forming a coating film excellent in waterproofness and acidproofness, and a resin applicable in the aqueous paint composition.SOLUTION: An aqueous paint composition contains a modified urethane resin containing a carbonyl group, and a thioether group and/or a thiourethane group, and a hydrazine derivative as a crosslinking agent reactive with the carbonyl group, the aqueous paint composition can be cured at an ambient temperature, and is excellent in storage stability of a paint, to be thereby usable as a one-pack type. The aqueous paint composition can form a coating film excellent in waterproofness, acidproofness and adhesion.
