(Problem) The high voltage can be applied to the internal conductor (heating element) only for a short time, thereby more surely suppressing the abnormality in the internal conductor (heating element), and improving the detection accuracy of the short circuit. (Solution) A high voltage higher than an applied voltage for normal use is applied to the inner conductor 3 (coil (3) (coil (3)) for a short period of time 31 between the outer conductor 2 and the inner conductor 3 (between the tube 21 and the coil 31) on the basis of a value varying in accordance with the current flowing in the inner conductor 3 The short-circuit abnormality is checked. This makes it possible to improve the detection accuracy of a short circuit or the like while suppressing the abnormality of the internal conductor 3 (coil 31). Further, since the high voltage is applied, the detection accuracy can be further improved.
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