The present invention can provide a heat-curable resin composition which is excellent in insulation property, heat resistance, and preservation stability. The heat-curable resin composition includes (A) cyanate ester compound having at least two cyanate groups in a molecule, (B) phenol curing agent including a resorcinol type phenol resin represented by the formula (1), (In the formula, n represents an integer from 0 to 10, each of R1 and R2 independently represents a monovalent group selected from a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an allyl group, and a vinyl group.), and (C) at least one compound selected from a tetraphenylborate of a tetra-substituted phosphonium compound and a tetraphenylborate represented by the formula (2). (In the formula, R3 represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a phenyl group, and n represents an integer from 1 to 3).