Abstract: A multi-layer winding comprising cylindrically-wound conductors and having different diameters are arranged concentrically. The layer windings are connected in series from inside to outside. Each layer winding has a layer insulator arranged on the inside thereof with a flange. Inwardly of the layer insulator and adjacent to the next inward layer winding is formed an oil gap functioning as a cooling-oil path. That oil-gap-equivalent part at and in the vicinity of the ends of the layer winding where the potential is maximum between adjacent layer windings is larger than the other parts thereof. This construction reduces the intensity of the electric field at the ends of each layer winding and eliminates partial discharge, thus improving the reliability and rendering the multi-layer winding compact and light in weight as a whole.