The present invention has features (1) to (3). The feature (1) is that “an active gas generation electrode group is formed in such a manner that a ground side electrode component supports a high-voltage side electrode component”. The feature (2) is that “stepped parts are provided in a discharge space outside region of a dielectric electrode in the high-voltage side electrode component, and project downward, and by a formation height of these stepped parts, the gap length of a discharge space is defined”. The feature (3) is that “the high-voltage side electrode component and the ground side electrode component are formed to have the thickness of a discharge space formation region relatively thin and the thickness of a discharge space outside region relatively thick”.