PURPOSE: To perform insulation processing being free from voids and having high reliability, by performing two processes of impregnation and setting, and by crushing, in the second process, the voids formed in the first process.

CONSTITUTION: In a method of insulation processing of the winding of an electric apparatus wherein a winding conductor is provided with an insulation layer formed by winding an insulating tape or sheet round and then is impregnated with thermosetting resin in vacuum and under pressure and taken out of the resin thereafter to be set by heating, each process of impregnation and setting is performed twice. In the second process, the feeding speed of the resin for impregnation is slowed down to 1/4W1/8 of that in the first process, while a process of application of pressure is omitted or performed for less than an hour under three atms or below.