A water blocking structure for an insulation-coated wire includes a heat-shrinkable tubular protective member that is closed at one end and that accommodates an intermediate portion of an insulation-coated wire that is bent in a folded-backward direction, and a resin material that is accommodated in the protective member and that penetrates the intermediate portion of the insulation-coated wire. A slit portion is formed by a cutting instrument in a coating of the insulation-coated wire within a region where the intermediate portion is bent in the folded-backward direction, and a water blocking agent penetrates the intermediate portion via this slit portion.