To provide a thermosetting coating film suitable for the clear coating of automobile parts and top clear coating of automobiles and having excellent appearance (smoothness, gloss, etc.), physical properties (hardness, scratch resistance, etc.), and chemical properties (acid resistance, solvent resistance, etc.), of practical level by a thin layer coating of 40-50 μm thick.

The thermosetting powder coating composition contains (A) an acrylic copolymer containing glycidyl group and (B) a polybasic carboxylic hardener having a basicity of ≥2. The ethylenic unsaturated monomer constituting the glycidyl-containing acrylic copolymer (A) contains styrene and glycidyl methacrylate as essential monomers and further contains other monomers. The glycidyl-containing acrylic copolymer has a weight-average molecular weight (Mw) of ≥2,500 and a designed glass transition temperature (Tg) of ≥50°C determined by Fox equation.