To provide an imide polyester resin which is excellent in surface curability and gives a cured product excellent in resistance to solvents, acids, and heat; a thermosetting resin composition using the same; and a cured product thereof.

This polyester resin is a reaction product of (a) an imide compound having two carboxyl groups and (b) an epoxy compound having two epoxy groups. The thermosetting resin composition essentially comprises (A) the imide-backbone polyester resin, (B) a cross-linker, and (C) a catalyst component.