In one embodiment of the present invention, an electrolyte membrane (110) is formed from an ionomer. A reduction catalyst to be used in a reduction electrode (120) contains Pt and/or Pd. An electrode for oxygen generation use (130) contains a catalyst composed of a noble metal oxide such as RuO2 and IrO2. A generated hydrogen gas quantity measurement unit (36) measures the quantity of a hydrogen gas that passes through a pipe (31) together with an aromatic hydrocarbon compound or a nitrogenated heterocyclic aromatic compound and calculates the quantity (F1) of the generated hydrogen gas on the basis of the measurement value. A control unit (60) gradually increases the voltage between the reduction electrode (120) and the electrode for oxygen generation use (130) within a range that fulfills the requirements represented by the formulae: F1 ‰¤ F0 and V CA > (V HER - allowable potential difference) wherein V TRR represents the standard oxidization-reduction potential of the aromatic hydrocarbon compound or
