Carboxyl group-containing polyester and thermosetting resin composition comprising same

A carboxyl group-containing polyester which provides a cured product that simultaneously satisfies thermosetting properties, long term insulation reliability, flexibility, plating resistance and copper foil adhesion. The carboxyl group-containing polyester has a number average molecular weight of over 10000 and 50000 or less and has a resin acid value of 1200 equivalent/10 6 g or more, and a polycarbonate diol which is a raw material has multiple types of alkylene chains in which at least two types of starting diols are copolymerized and has a number average molecular weight of 700 to 2300.