A discharge unit (20) is provided with: a discharge electrode (70) a counter electrode (60) disposed opposite the discharge electrode (70) and an insulating member (41) having a continuous surface from the discharge electrode (70) to the counter electrode (60). On one side of a discharge region of the discharge electrode (70) there is provided a wall portion (90) for suppressing the attachment of contaminating substances onto the surface of the insulating member (41).