A crystalline epoxy resin is modified to provide an epoxy resin composition capable of producing a cured product with excellent cured product properties.
The modified epoxy resin composition comprises compound A having in its molecule a functional group represented by formula (1):

(where each of R 1 and R 2 is an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an aralkyl group, a heterocyclic group, or a halogenated, aminated or nitrated derivative thereof), and compound B having a glycidyl group in its molecule. The compound A is preferably a compound resulting from replacement of from at least one to at most n glycidyl groups among n glycidyl groups in a molecule (where n is an integer of from 2 to 16) with the functional group of the formula (1). The compound B is preferably a compound having n glycidyl groups (where n is an integer of from 2 to 16) in its molecule.