PURPOSE: To apply excellent insulation treatment by a method wherein an insulation tape prepared by forming a mica layer on one surface of lining material and an layer for accelerating the setting of an epoxy resin on the other is wound round a conductor with the accelerator layer outside and thereby the conductor is impregnated under vacuum with the epoxy resin containing a prescribed hardener.

CONSTITUTION: The mica layer 2 is formed on one surface of the lining material 1 by bonding 3 composite mica thereto, while the setting accelerator layer 5 is formed on the other surface of the lining material by applying thereon isocyanate resin 4 and later the epoxy resin setting accelerator of imidazole dissolved in a solvent and drying the same. The insulation tape A thus prepared is wound round the outer periphery of the winding conductor B with the accelerator layer outside, while the outer periphery of a coil is wound up in the same way, and thus the conductor is impregnated under vacuum with the epoxy resin, which is further heated and dried. By this constitution, the resin near the layer 5 is first set to prevent the resin from flowing out and thereby the lowering of insulation is prevented.