PURPOSE: To suppress the generated potential at lower level by a method wherein a semiconductive layer is composed of the first semiconductive layer covering the whole periphery of an insulating layer in the peripheral length direction of the title driving coil at specific resistance value and the second semiconductive layer at the lower resistance value than that of the first semiconductive layer arranged in contact with the same semiconductive layer in the specific length part in the peripheral length direction of said driving coil.

CONSTITUTION: This driving coil 12 is provided with an interlayer insulator 2 interposed between wound up coil conductors 1, a bind layer 3 provided in the coil conductor bonding direction, insulating layer 4 and a semiconductive layer 11. On the other hand, the semiconductive layer 11 of this driving coil 12 is composed of a semiconductive layer 9 covering the whole periphery of the insulating layer 4 in the periphery length direction of the driving coil 12 at specific resistance value and another semiconductive layer 10 at the lower resistance value than that of the semiconductive layer 9 arranged in contact with the same layer 9 in the specific length part in the peripheral length direction of the driving coil 12. Through these procedures, when the driving coil 12 is impressed with a voltage, the potential generated in the semiconductive layers can be suppressed thereby enabling the discharge occurrence to be prevented.