A heat-curable epoxy resin composition is a mixture in which an epoxy compound represented by formula (al), a polyisocyanate, a bisphenol type liquid epoxy resin and an epoxy resin curing agent are blended. An amount of the epoxy compound, per 100 parts by mass of all the epoxy resin blended in the heat-curable epoxy resin composition, is 5 parts by mass or more.; 展开▼