A latent epoxy resin curing agent is provided which can be manufactured without using an amphiphilic polymer compound requiring a painful trial and error selection process, 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, the adduct particles of the epoxy-based compound and the imidazole-based compound are coated with an ethyl cellulose film, and the surface thereof is crosslinked with a polyfunctional isocyanate compound. The epoxy-based compound, the imidazole-based compound, and ethyl cellulose are dissolved in a predetermined saturated hydrocarbon-based solvent under stirring and heating. Then, the epoxy-based compound and the imidazole-based compound are subjected to adduct reaction to obtain a slurry of the adduct. After the slurry was cooled, the polyfunctional isocyanate compound is added thereto to crosslink the ethyl cellulose film.