The present invention relates to a waterproofing structure for an insulation-coated electrical wire that includes a tubular protection member and a resin material that is accommodated in the protection member. An exposed conductor section includes a plurality of bare wires bent to double back in a reverse direction in the protection member, the protection member including a tubular section that surrounds the exposed conductor section and the pair of on intermediate ends of the coating tube that are adjacent to both ends of the exposed conductor section; and a closed section that is distanced from the exposed conductor section in the axial direction and closes one end of the tubular section. The resin material is made of a thermosetting resin that is cured, between the protection member and the insulation-coated electrical wire, while closely fitting to the closed section, the exposed conductor section, and the pair of intermediate ends.