Abstract: A method of manufacturing a wound core formed by winding a long, narrow strip of magnetic material, used for transformers reactors or other devices. One belt shaped magnetic material is cut along one polygonal line that extends in the longitudinal direction of the strip of material so as to form two continuous strips each of which consists of a sequential connection of individual portions of winding material, each of which portion has a shape of a long, narrow pentagon wherein the width changes to be narrow at a leading end thereof, wide in the middle part and narrow again at the trailing end. One side edge of each continuous strip forms a straight line and the other edge forms a polygonal line. One of the portions of winding material is wound, while maintaining the center of the strip at a fixed position in the width direction, to form a wound core with a hexagonal cross-section. As result, there is no waste of material and connection of separate strips of material during the winding is unnecessary.