A thermosetting powder paint composition is disclosed which can realize simultaneous manifestation of I) excellent stability before film forming (in storage), II) excellent low temperature melting property/low temperature curing property in forming a film, and III) excellent film properties and physical properties after film forming;and which comprises (A) a copolymer component which is obtained by radical polymerization in a reaction system containing (a-1) an ethylenically unsaturated monomer having a glycidyl group and a unsaturated double bond in the molecule, (a-2) styrene, and (a-3) the other monomer in a specific condition, (B) a curing agent component which is a linear acid anhydride of an aliphatic divalent carboxylic acid having a specific structure, and (C) a curing catalyst component having a specific structure.