To provide a quick-drying aqueous coating composition which is a one-pack type, good in storage stability, fast in the drying after the application, and good in adhesion to the coated surface, abrasion resistance and water resistance.

The one-pack type aqueous coating composition, which uses a phosphate compound represented by general formula (1) or (2) as a plasticizer of a quick-drying aqueous coating, is excellent in storage stability, fast in the drying after the application and has all the characteristics required for a road marking paint, such as water resistance and adhesion. In general formulas (1) and (2), R1, R2 and R3, which may be the same or different, are each a 1-18C aliphatic hydrocarbon group, aromatic hydrocarbon group, alicyclic hydrocarbon group, haloalkyl group or haloalkylphenyl group; A is the residue of a 1-6C aliphatic hydrocarbon or an aromatic hydrocarbon; and B is a 1-18C aliphatic hydrocarbon group, or the residue of an aromatic hydrocarbon or an alicyclic hydrocarbon.