The object of the present invention is to provide an epoxy resin composition capable of realizing low dielectric constant and low dielectric dissipation factor, which is suited for use as a latest current high-frequency type electronic component-related material, without deteriorating heat resistance during the curing reaction. A phenol resin, which has the respective structural units of a phenolic hydroxyl group-containing aromatic hydrocarbon group (P) derived from phenols, an alkoxy group-containing condensed polycyclic aromatic hydrocarbon group (B) derived from methoxynaphthalene and a divalent hydrocarbon group (X) such as methylene and also has a structure represented by -P-B-X- wherein P, B and X are structural sites of these groups in a molecular structure, is used as a curing agent for the epoxy resin, or a phenol resin as an epoxy resin material.