The present invention provides an acid anhydride ester obtained by esterifying cyclohexane-1,2,4-tricarboxylic acid-1,2-anhydride and a composition of the ester, and a heat-curable resin composition and a cured product of the composition. _Provided is an epoxy resin composition using the acid anhydride ester as a curing agent for an epoxy resin, the epoxy resin composition having, for example, the following properties (1), (2), and (3): (1) the epoxy resin composition has a low viscosity at room temperature, so the components of the composition can be favorably blended with each other, (2) the acid anhydride ester has a low vapor pressure at curing temperature, so no evaporation loss occurs after curing, and the intended design of blend is capable, and (3) a cured product to be made from the composition is colorless and transparent, and changes its color to a small extent even when the product is irradiated with light or heated for a long time period. The composition is suitably used as, for example, an encapsulant for a photoelectric conversion element such as a blue LED or a white LED, a molded article, a coating, or an adhesive.