A microencapsulated latent hardener for epoxy resins which comprises cores (C) and shells (S) with which the cores are covered, characterized in that the cores (C) are ones formed from, as a starking material, particles of an epoxy resin hardener (H) comprising an amine adduct (A) and a low-molecular amine compound (B) as major ingredients and that the shells (S) have on the surface thereof connecting groups (x), (y), and (z) which absorb infrared. Also provided is an epoxy resin composition containing the hardener.