PURPOSE: To wind a conductor under the application of higher tension and obtain a coil with high mechanical strength and excellent insulation characteristics by a method wherein, when the 1st winding layer is formed, expanding bodies are provided to a cooling duct part between this 1st winding layer and an inside insulation cylinder or an inside coil and the conductor is prevented from slipping by friction effect of the expansion pressure.

CONSTITUTION: Duct spacers are put on an insulation cylinder 1 at a certain interval to form a cooling duct part 2 and the 1st winding layer is formed by winding a conductor from the beginning 15(1) to the finish 15(n). Then, into several positions in the cooling duct part 2 formed between the insulation cylinder 1 and the 1st winding layer 15, expanding bodies 16 are inserted at the constant interval along the circumference direction. After the bodies are inserted and fixed, pressurized air is introduced into the bodies and when the pressure reaches a suitable value (enough pressure to produce necessary friction in order to fix the winding layer), air introduction is cut and the body is sealed by closing a cock device 18. After the 1st winding layer 15 is fixed, the 2nd and other layers 15 are wound with necessary interlayer insulation 19 and with application of tension to form an inner coil 3.