To provide an epoxy resin composition which allows curing to sufficiently proceed even under a comparatively low heat curing condition, does not involve any excessive heat generation even when a molded article with a large size or thickness is manufactured, and gives good physical properties.

The epoxy resin composition contains: an epoxy resin curing agent containing a polyamino composition that is obtained with a styrene reaction rate of 1.2 to 1.5 mol based on 1 mol of a polyamino compound A represented by formula (1), and essentially contains a mixture of a polyamino compound B which is an adduct, of which the structures of side chain groups are different from each other, represented by formula (2); and an epoxy resin. The formula (1) is H2N-CH2-A-CH2-NH2, wherein A is a phenylene group. The formula (2) is R1R2N-H2C-A-CH2-NHR3, wherein A is a phenylene group; and R1 to R3 are a hydrogen atom or a phenethyl group, with the proviso that R1 to R3 may be the same or different, but at least one of R1 to R3 is a phenethyl group.