An ionizer includes an electrode shaft, a fixing bar, a driver, and a controller. The electrode shaft includes first and second electrode rows, the first electrode row having a plurality of ionizer electrodes arranged in a first direction and the second electrode row having a plurality of ionizer electrodes arranged in the first direction and spaced apart from the first electrode row. The fixing bar includes a discharge area facing an object to be processed, and accommodates the electrode shaft so a single electrode row is disposed in the discharge area. The driver is inside the fixing bar so as to be coupled to both end portions of the electrode shaft, and controls a position of the electrode shaft. The controller controls the driver to replace the electrode row disposed in the discharge area with another electrode row according to a previously input replacement condition.