PURPOSE: To avoid the dielectric breakdown at the transition region by connecting through the transition region made of flexible conductor coated with the tubular insulation cap around it, when connecting plural numbers of spirally wound coil in series.

CONSTITUTION: On connecting each of the spirally wound coil conductors 11 to one another, the connection is performed by means of the transition region 15 made of multi pieces of flexible conductor each of which are coated with flexible tubular insulation caps 18. At this time, the nose of the cap 18 is protruded a little beyond the nose of the conductor 16 and fitted to the initial end of the conductor 11 through a slight gap 19 so as to permit sliding. Furthermore, a flexible insulator 13 such as rubber is filled therein, to enhance the insulation, if necessary. In such a way, even if relative displacement is generated among each of conductors 11 by the electromagnetic force, the displacement is absorbed by the elastic deformation, of the transition region 15 thus resulting in no dielectric breakdown in the transition region 15.