Disclosed is a charge transfer complex capable of obtaining a curable resin composition having an excellent balance between curability and storage stability when used as an epoxy-resin curing agent. The charge transfer complex has an imidazole moiety as an electron donor moiety. The charge transfer complex may be an assembly wherein electrons included in a compound (a) having an imidazole moiety are accepted by a compound (b) having an electron acceptor moiety, or may be a compound having an imidazole moiety and an electron acceptor moiety in its molecule, and the electron acceptor moiety accepts electrons included in the imidazole moiety.