The present invention suppresses the reduction of a discharge product from a first and a second discharge electrode. A partition plate (14) between positive side and negative side discharge electrodes (11, 12) has a height higher than the upper end of the positive side and negative side discharge electrodes (11, 12) and is parallel to the air-flow direction. A downstream side end of the partition plate (14) is present at: the same position as the most downstream side end of the electrodes which is present on the most downstream side among the downstream side ends of the positive side and negative side discharge electrodes (11, 12) and an induction electrode; or at the upstream side of the most downstream side end of the electrodes.