PURPOSE: To treat a winding body with varnish without attaching vanish on the outer circumferential surface of a stator by covering the stator with a double bag having airtightness, arranging a balloon so as to be brought into contact with the end face of a core as a ring-shaped clamp on the outside of the inner bag and preventing the intrusion of varnish onto the outer circumferential surface of a core when pressure in the bag is decompressed.

CONSTITUTION: A stator 3 containing a winding body 2 is housed in an airtight inner bag 6, and a required quantity of vanish 5 is received in the inner bag 6. A ring-shaped balloon 8 is disposed outside the inner bag 6 on the end face of a stator core 1, and the outer circumference of the balloon 8 is covered with an outer bag 7 and the stator 3 is covered with a double bag. The mouth section 6a of the inner bag 6 and the mouth section 7a of the outer bag are connected to a vacuum pump, the insides of the inner bag 6 and the outer bag 7 are decompressed, the inner bag 6 is fast stuck on the inner and outer circumferential surfaces of the stator 3, and the stator 3 is impregnated with internal vanish 5. The ring-shaped balloon 8 is expanded and pushed against the stator core 1 at that time, the path of vanish 5 onto the outer circumferential surface of the stator core 1 is clogged, the intrusion of vanish is prevented, and the adhesion of vanish 5 is obviated.