PURPOSE: To prevent voids from being generated in a coil when insulating varnish is completely immersed in vacuum by coating one or both sides of a flat type wire with the varnish, and so winding the wire on a bobbin as to superpose the surfaces coated with the varnish.

CONSTITUTION: The end of a flat type wire 12 is secured to a bobbin 17, and the bobbin 17 is rotated in this state. The wire 12 is introduced from a flat type wire drum 11, and the lower surface of the wire 12 is intermittently coated with insulating varnish 15 by the projection 16a of a coating roller 16. The wire 12 coated with the varnish 15 is so sequentially wound as to superpose the surface coated with the varnish 15 on the portion previously wound on the bobbin 17. At this time, the varnish 15 is thinly spread on both surfaces of the wires 12 to be superposed to be filled without gap on the both surfaces of the wire 12 to be superposed.