PURPOSE: To ensure the dielectric strength of a winding and to improve the cooling effect of coupling bolts by a method wherein an insulating film, which has a fan-shaped section and is notched on the opposite side to its side to oppose to the winding, a cylindrical insulating coating not having a notch part and an insulating coating, which has a fan-shaped section and is notched its side to oppose to the winding, are coupled together.

CONSTITUTION: The title insulation structure is formed into a constitution, wherein an opposite side notch insulating film 51 is notched its opposite side to a winding 2, the surfaces of coupling bolts 4 are exposed, a due opposite side notch insulating coating 53 is notched its side to opposite to the winding 2 and the surfaces of coupling bolts 4 are exposed. A cylindrical insulating coating 52 is positioned at roughly the central part of the structure in the height direction and is coupled with the insulating film 51 and the insulating coating 53. A coupling bolt insulating coating 5A is maintained in a state that it is installed in such a way that it may be separated from the bolts 4. Thereby, while a dielectric strength between the bolts and the wiring is ensured, the cooling effect of the bolts 4 can be improved and the reliability of an induction electrical apparatus can be improved.