The problem to be solved by the present invention is to provide a polyester resin excellent in various properties wherein the film formability is good, film fracture (hairs) and scraping (galling) are not easily generated in the drawing/ironing process when applied to a metal-sheet-coating polyester film, the film surface is not damaged when used as the inner-surface film for a metallic can, and the metallic can is hardly corroded (dent resistance), by dropping or external impact (denting), after a product is made by enclosing contents into the can.
The copolyester resin of the present invention is characterized by comprising, as the constituent units, 50 to 93 mass % of (A) ester oligomer with the number-average molecular weight of 700 or lower and consisting of a dicarboxylic acid unit (a1) containing 70 mole % or more of the terephthalic acid component and a diol unit (a2) containing 70 mole % or more of the ethylene glycol component; and 7 to 50 mass % of (B) polyester polyol with the number-average molecular weight of 1500 to 3000 and consisting of a hydrogenated dimer acid unit (b1) and a 1,4-butanediol unit (b2).