The present invention relates to a composition containing as a main component, an epoxy resin which has a structure comprising a polyaryleneoxy structure such as polynaphthylene oxide as a main skeleton, (methyl)glycidyloxy group and aralkyl group being introduced on an aromatic ring of the polyaryleneoxy structure, and which has low viscosity, according to the present invention, there can be provided an epoxy resin composition which can impart remarkably excellent flame retardancy and dielectric characteristics to a cured article and a cured article thereof, an epoxy resin, a phenol resin as an intermediate of the epoxy resin, and a method for producing the epoxy resin.