A first separator that prevents a pair of electrodes from short-circuiting each other is provided on end parts of the pair of electrodes in a longitudinal direction thereof, a first molded resin part that covers the first separator is provided on an end part of an insulation tube in a longitudinal direction thereof, a part of the first separator) on one side in a direction intersecting the longitudinal direction and another part of the first separator on the other side in the direction intersecting the longitudinal direction are each exposed to outside. When the first separator is embedded in the first molded resin part through insert molding, the first separator can be supported by a lower mold and an upper mold, portions of the first separator supported by the pair of molds at this time are portions exposed to outside.