A purpose of the present invention is to provide a thermosetting resin composition which is free from the generation of a free isocyanate even if a carbodiimide compound is used, and which is capable of providing a cured resin that has high heat resistance. Another purpose of the present invention is to provide: a thermosetting resin composition which can have a lower curing temperature and is cured in a short time, and which provides a cured resin that has a high glass transition temperature; and a cured resin of this thermosetting resin composition. The present invention is a thermosetting resin composition which contains: (A) an epoxy resin (component A); and (B) a cyclic carbodiimide compound (component B) which has a cyclic structure represented by formula (B-i) that has one carbodiimide group wherein a first nitrogen atom and a second nitrogen atom are bonded by a bonding group, and in which the cyclic structure is composed of 8-50 atoms, and/or (b) a polyvalent amine curing agent (component b) which is represented by formula (b-i). (In formula (B-i), Q represents an aliphatic group, an alicyclic group, an aromatic group or a divalent to tetravalent bonding group that is a combination of the preceding groups, and may contain a heteroatom or a substituent.) (In formula (b-i), each of Ar1-Ar4 independently represents a phenylene group or naphthalene-diyl group, which may be substituted by a substituent.)