Provided is a microcapsule-based hardener for an epoxy resin, which have a core (C) formed using a hardener (H) for the epoxy resin as a starting material and a shell (S) for covering the core (C) therewith. Since it is characterized in that the hardener (H) for the epoxy resin has an average particle size exceeding 0.3 μm and not greater than 12 μm; a content of a small-particle-size hardener for epoxy resin defined to have a particle size 0.5 time or less of the average particle size of the hardener (H) for the epoxy resin is from 0.1 to 15%; and the shell (S) has, on the surface thereof, a binding group (x) capable of absorbing infrared rays having a wave number of from 1630 to 1680 cm−1, a binding group (y) capable of absorbing infrared rays having a wave number of from 1680 to 1725 cm−1, and a binding group (z) capable of absorbing infrared rays having a wave number of from 1730 to 1755 cm−1, it is excellent in storage stability and at the same time, in reaction rapidity.