PURPOSE: To reduce and eliminate leakage magnetism by providing a lead wire about in paralled with a hot wire so that a direction of an electric current electrifying the lead wire becomes opposite to that of the hot wire.

CONSTITUTION: Hot wires 3 are arranged on a pattern of laterally parallel wiring, both ends of these hot wires 3 are connected with a positive power source side bus bar 4 and a negative power source side bus bar 5 respectively, and power supply lead wires 6 and 7 are connected with about the center of the bus bars 4 and 5. And the power supply lead 6 is provided about in parallel with the hot wire 3 so that a direction of an electrifying the lead wire 6 becomes opposite to that of the hot wire 3.