NOVELTY - A hardening agent consists of a core containing an epoxy-resin hardener and a shell which covers the core. The epoxy-resin hardener contains an amine adduct obtained by reacting an epoxy resin (e1) and an amine compound. The shell has bonding group (x) which absorbs infrared rays of wavenumber 1630-1680 cm-1 in an infrared absorption spectrum, bonding group (y) which absorbs infrared rays of wavenumber 1680-1725 cm-1, and bonding group (z) which absorbs infrared rays of wavenumber 1730-1755 cm-1 on the surface.    USE - Hardening agent is used in hardening-agent compositions for microcapsule-type epoxy resins and one-component epoxy resin compositions used for processed products (all claimed) anisotropically conductive films, paste-form compositions, film-form compositions, adhesive agents, pastes used for joining, films used for joining, electroconductive materials, anisotropically conductive materials, insulating materials, sealing materials, coating materials, coating compositions, prepregs, thermally conductive materials, separator materials of fuel cells, and overcoat materials of flexible wiring boards (all claimed).    ADVANTAGE - The hardening agent has excellent storage stability and low-temperature rapid hardening property. The agent provides anisotropically conductive films having excellent connection reliability.    DETAILED DESCRIPTION - A hardening agent consists of a core containing an epoxy-resin hardener and a shell which covers the core. The epoxy-resin hardener contains an amine adduct obtained by reacting an epoxy resin (e1) and an amine compound, and has an overall amine titer value of 370-1000 and an average particle diameter of more than 0.3 mu m and 12 mu m or less. The shell has bonding group (x) which absorbs infrared rays of wavenumber 1630-1680 cm-1 in an infrared absorption spectrum, bonding group (y) which absorbs infrared rays of wavenumber 1680-1725 cm-1, and bonding group (z) which absorbs infrared rays of wavenumber 1730-1755 cm-1 on the surface. INDEPENDENT CLAIMS are included for the following:    (1) hardening-agent composition containing an epoxy resin and the hardening agent, in a weight ratio of 100:10-10:1000;    (2) one-component epoxy resin composition comprising the hardening agent, an epoxy resin, and a high-solubility epoxy resin. The solubility parameters of the basic structure of the high-solubility epoxy resin are 8.65-11. The molecular weight between crosslinking of the basic structure is 105-150. The abundance of a diol terminal impurity component is 0.01-20 %mass with respect to a basic structure component. The mass ratio of hardening agent for microcapsule-type epoxy resins and epoxy resin is 100:10-100:1000. The mass ratio of epoxy resin and high-solubility epoxy resin is 100:0.1-100:1000. The total chlorine content is 2500 ppm or less; and    (3) anisotropically conductive film comprising electroconductive particles, epoxy resin (b) having epoxy ring(s), an organic binder (c) consisting of resin, and the hardening agent.