A subject of the present invention is to provide a one-pot type epoxy resin composition having both high curability and storage stability and a latent hardener for obtaining the same, and to provide anisotropic conductive materials, conductive adhesive materials, insulating adhesive materials, sealing materials, and the like which have high storage stability, solvent resistance and humidity resistance and can provide high connection reliability, adhesive strength and high sealing properties even under curing conditions such as low temperatures or short periods of time. The present invention relates to a latent hardener for epoxy resins in which a hardener (A) for epoxy resins is covered with a film (c1) obtained by reacting an isocyanate component (b1) comprising a low molecular bifunctional aliphatic isocyanate compound in an amount of 1% by mass or more and 95% by mass or less with an active hydrogen compound (b2), and to a one-pot type epoxy resin composition using the same.