An epoxy curing agent comprising a heterocycle-containing compound having a structure represented by any of the following formulae (2) through (9) ##STR7## wherein in formula (2), "a" represents an integer of 3 to 200, A.sup.1 represents at least one member selected from the group consisting of alkylene group which is either substituted by --X--Z or unsubstituted, arylene group, arylalkylene group, haloalkylene group and a residue available on ring-opening polymerization of a glycidyl ether;
- wherein in formula --X--Z, X represents a divalent hydrocarbon group which may optionally have one or more linkages selected from the group consisting of ether, imino, amide, urethane, urea and sulfide linkages and Z represents a heterocyclic group of the formula (1):
- ##STR8## wherein R.sup.1 and R.sup.2 may be the same or different and each represents hydrogen atom, straight-chain or branched C.sub.1 to C.sub.6 alkyl or alkenyl, or C.sub.6 to C.sub.8 aryl;
- or R.sup.1 and R.sup.2, taken together with the adjacent carbon atom, represents C.sub.5 to C.sub.7 cycloalkyl;
- R.sup.3 represents C.sub.1 to C.sub.10 alkylene;
- wherein at least three of A.sup.1 in formula (2) represent alkylene group substituted by --X--Z,
- wherein in formula (3), "b" represents an integer of 3 to 200, and Q.sup.1 represents at least one member selected from the group consisting of hydrogen atom, alkyl group, aryl group, haloalkyl group, haloaryl group, alkoxycarbonyl group, acetoxy group and --X--Z;
- wherein at least three of Q.sup.1 in formula (3) represent --X--Z;
- wherein in formula (4), "c" represents an integer of 2 to 200, and A.sup.2 and A.sup.3 may be the same or different and each represents at least one member selected from the group consisting of alkylene group which is either substituted by --X--Z or unsubstituted, arylene group which is either substituted by --X--Z or unsubstituted, aralkylene group and haloalkylene group;
- wherein at least three of A.sup.2 and A.sup.3 in formula (4) represent at least one species selected from the group consisting of alkylene group substituted by --X--Z and arylene group substituted by --X--Z;
- wherein in formula (5), "d" represents an integer of 3 to 200, and A.sup.4 represents at least one selected from the group consisting of alkylene group which is either substituted by --X--Z or unsubstituted, arylene group which is either substituted by --X--Z or unsubstituted, aralkylene group and haloalkylene group;
- wherein at least three of A.sup.4 in formula (5) represent at least one species selected from the group consisting of alkylene group substituted by --X--Z and arylene group substituted by --X--Z;
- wherein in formula (6), "e" represents an integer of 2 to 200, and A.sup.5 and A.sup.6 may be the same or different and each represents at least one selected from the group consisting of alkylene group which is either substituted by --X--Z or unsubstituted, arylene group which is either substituted by --X--Z or unsubstituted, aralkylene group and haloalkylene group;
- wherein at least three of A.sup.5 and A.sup.6 in formula (6) represent at least one species selected from the group consisting of alkylene group substituted by --X--Z and arylene group substituted by --X--Z;
- wherein in formula (7), "f" represents an integer of 2 to 200, and A.sup.7 represents at least one selected from the group consisting of alkylene group which is either substituted by --X--Z or unsubstituted, arylene group which is either substituted by --X--Z or unsubstituted, aralkylene group and haloalkylene group;
- wherein at least three of A.sup.7 in formula (7) represent at least one species selected from the group consisting of alkylene group substituted by --X--Z and arylene group substituted by --X--Z;
- wherein in formula (8), "g" represents an integer of 3 to 200, and A.sup.8 represents at least one selected from the group consisting of alkylene group which is either substituted by --X--Z or unsubstituted, arylene group which is either substituted by--X--Z or unsubstituted, aralkylene group and haloalkylene group;
- wherein at least three of A.sup.8 in formula (8) represent at least one species selected from the group consisting of alkylene group substituted by --X--Z and arylene group substituted by --X--Z;
- wherein in formula (9), "h" represents an integer of 3 to 200, Ar represents at least one selected from the group consisting of aryl group, and Q.sup.2 represents at least one species selected from the group consisting of hydrogen atom, epoxy group and --X--Z;
- and wherein
- at least three of Q.sup.2 in formula (9) represent --X--Z.