PURPOSE: To provide the titled compsn. which has excellent impact resistance and adhesion to metallic substrates, gives a coating film having excellent surface properties, has a low baking temp. and allows the substrate to be preheated at low temp. during coating, consisting of a polyester copolymer, a crystallization accelerator and a leveling agent.

CONSTITUTION: A dicarboxylic acid component contg. 40W60mol% of terephthalic acid is reacted with a diol component contg. at least 70mol% of 1,4-butanediol in the presence of a catalyst at 150W220°C to obtain a polyester copolymer (A) having as melt peak temp. of 100W150°C as measured by differential thermal analysis. 0.01W1pt.wt. ultrafine talc powder having an averge particle size of 4μ or below as a crystallization accelerator, 0.05W2pts.wt. acrylic copolymer contg. silica powder as a leveling agent and optionally, additives such as pigment, weathering agent, etc., are blended with 100pts.wt. component A. the mixture is melt-kneaded, cooled, pulverized and classified to obtain a thermoplastic polyester powder coating compsn. having a particle size of 60W300μ.