To introduce electric energy necessary for the decomposition of nitrogen oxides, sulfur oxides, etc., efficiently into flue gas.

In a flue gas decomposing apparatus in which flue gas containing nitrogen oxides, sufur oxides, etc., is led into an electric discharge space, and the contained nitrogen oxides and sulfur oxides are decomposed by applying a high voltage to discharging electrodes, the discharging electrodes are equipped with a large diameter electron generating electrode 13 and a small diameter electron accelerating electrode 11.