PURPOSE: To prevent the formation of a pleat-shaped excessive insulating layer in the coil-end part of a winding and to prevent the damage to a bag in a method for impregnating a winding body with varnish by the use of a bag.

CONSTITUTION: A ring-shaped buffer member 20 is mounted on the outer periphery of the coil-end part 13a of a stator 11. The buffer member 20 is composed of a material having elasticity and good release properties from varnish 23 and adheres in the manner of following the inner peripheral face of the coil-end part 13a and the end face of a stator core 12. In this mounting state, there is no large difference in level in the outer peripheral shape of the stator 11. in a state where a balloon-shaped bore barrier member 21 is arranged in the inner peripheral part of the stator 11, the stator is contained in a gas-tight bag 22, in which the varnish 23 is contained, and subjected to decompression in a closed tank. After the mouth 22a of the bag 22 is sealed, the gas pressure in the tank is restored to atmospheric pressure so that the bag 22 adheres to the stator 11 and to the outer peripheral face of the buffer member 20 and a winding is impregnated with the varnish 23 pushed into a narrow space between the strands, etc., of the winding 13.