A latent epoxy resin curing agent is provided which exhibits excellent solvent resistance and low-temperature fast-curing ability, and contains an imidazole-based compound as a main component. In the latent epoxy resin curing agent containing the imidazole-based compound as a main component, adduct particles formed through adduct reaction of an epoxy-based compound with the particulate imidazole-based compound are coated with an ethyl cellulose film. Furthermore, the surfaces of the adduct particles may be crosslinked with a polyfunctional isocyanate compound. A mixture of the epoxy-based compound, the particulate imidazole-based compound, and ethyl cellulose in a predetermined saturated hydrocarbon-based solvent is heated under stirring. Then, the epoxy-based compound and the particulate imidazole-based compound are subjected to adduct reaction to give a slurry of the adduct. After the slurry is cooled, the latent epoxy resin curing agent is filtrated.