A discharge electrode (70) is constituted of a metal material and has a plate shaped electrode support plate (71) and a plurality of discharge parts (73 74) arranged along side edge parts of the electrode support plate (71) and supported by the side edge parts of the electrode support plate (71) so as to face a counter electrode (60). An insulating member (41) has a support part (47) for supporting a middle region (71a) of the electrode support plate (71) between discharge parts (73a 74a) disposed on both ends out of the plurality of discharge parts (73 74).