To provide an epoxy resin curing agent of a low viscosity and a long pot life to be produced at a low cost, an epoxy resin composition including the epoxy resin curing agent, and an epoxy resin cured product with excellent mechanical properties produced by curing the epoxy resin composition.

The epoxy resin curing agent includes (A) a non-modified polyamino compound having two or more amino groups in the molecule and an active hydrogen derived from the amino groups, and (B) a polyamino compound subjected to phenethylation, represented by general formula (2), (wherein W is a phenylene group or a cyclohexylene group, at least one of R¹, R² and R³ is a hydrogen atom, and the others are a phenethyl group).