PURPOSE: To provide an ideal stage-insulating material, by using an insulating tape and an efficient layer insulator obtained by combining insulators other than this.

CONSTITUTION: An end of wire 2 is pulled out of insulated cylinder 1 in its axial direction, forming lead wire 2a. The end part of lead wire 2a is wound around insulated cylinder 1. At the end of each layer, wire 2 shifts to the upper layer and is wound concentrically. The terminating end of wire 2 is formed in a similar manner as the beginning end, forming lead wire 2d. Thin leaf insulators are placed between layers, each wound by wire 2. Layer insulator 4, which is slightly longer than the circumferential length of wire 2 and of uniform thickness is combined with an insulating layer consisting of thin leaves of a certain width. Insulating tape 6 and the leaf layer are provided over the entire length of the coil. End-part insulator 3, which is matched to the circumferential length of each layer, is inserted into the end of each layer, wound by wire 2.