Provided are (i) a one-pack epoxy resin which exhibits excellent storage stability in terms of not only composition viscosity but also flowability and (ii) use thereof. The one-pack type epoxy resin composition, contains, as main components, (A) epoxy resin; (B) a modified aliphatic polyamine compound; and (C) inorganic filler treated with a long-chain hydrocarbon-group containing compound. Therefore, the present invention achieves (i) the one-pack type epoxy resin composition which exhibits the excellent storage stability in terms of not only the viscosity but also the flowability and (ii) use thereof.