To provide a method for making the addition ratio of inorganic filler for improving the heat resistance of resin to be high in the end at the vacuum- impregnating of silicon resin into a coil, to improve the heat resistant temperature of the coil and to provide the coil having heat resistance and reliability.

A coil 4 is put in a container 7 with an inorganic filler 6 and its entirety is vibrated to the right and left. Inorganic filler 6 is filled in the coil 4 and the coil 4 is immersed in silicon resin with inorganic filler 6. Then, vacuum impregnation is executed. A method for putting in the coil in the container with an inorganic filler, fixing only the coil, vibrating it vertically or to the right and left and filling the coil with the inorganic filler may be adopted as a different means.