Disclosed herein is a heat-hardenable paint composition comprising a base resin, wherein the base resin comprises (A) a lactone modified resin comprising hydroxyl groups, wherein 20 to 70 weight percent of the structural units are based on the lactone compound, and the hydroxyl group value is from 50 to 400 mgKOH/g, and (B) an acrylic resin comprising hydroxyl groups and cyclic structures, wherein 10 to 80 weight percent of structural units are based on a radically polymerizable monomer comprising a cyclic structure, the hydroxyl group value is from 50 to 150 mgKOH/g, and the crosslinking resin is an isocyanate compound, wherein the weight ratio of the solid fractions of (A):(B) in the base resin is from 95:5 to 20:80.