Abstract: A transformer is disclosed which has a primary and a secondary winding disposed concentrically around a core via a flanged bobbin. Each winding has a conductor wire which is doubly or, preferably, triply sheathed with insulating tapes of different widths. The first or inmost insulating tape is wound overlappingly in a first direction around the conductor wire without being bonded thereto. The second or intermediate insulating tape, less in width than the first, is wound overlappingly in a second direction, opposite to the first direction, over the first insulating tape and bonded thereto via a preformed adhesive layer on the second insulating tape. The third or outmost insulating tape, still less in width than the second, is wound overlappingly in the first direction over the second insulating tape and bonded thereto via a preformed adhesive layer on the third insulating tape. The ratio of the overlap of each tape to the tape width becomes progressively less from the inmost toward the outmost tape.