A thermosetting powder coating composition has an average particle diameter of entire particles is within a range from 5 to 50 &mgr;m, an average circularity of the particles is 0.90 or more, and a circularity of particles having a maximum number frequency in circularity distribution is within a range from 0.98 to 1.00, prepared by spray-drying an organic solvent solution containing, as a coating film forming component, an epoxy group-containing vinyl copolymer (A) having a glass transition temperature of 40° C. or higher, an epoxy group-containing vinyl copolymer (B) having a glass transition temperature of 0° C. or lower and a polycarboxylic acid (C) as an essential component.