In the vicinity of the blowout outlet, direct discharge may occur between the high-voltage electrode and the low-voltage electrode without passing through the dielectric substrate. Such discharge damages the high-voltage electrode, dielectric substrate, and low-voltage electrode, thereby mixing the materials constituting these components into the plasma as impurities. From a standpoint of discharge efficiency, it is advantageous to mount the high-voltage electrode at the front edge of the blowout outlet. However, this configuration allows the distance between the high-voltage electrode and the low-voltage electrode to become significantly shorter, causing creeping discharge on the dielectric substrate. Once the discharge occurs, it does not form dielectric barrier discharge, but moves on to direct discharge, thus an excessive discharge current flows, causing damage to the electrodes and eventually damage to the power supply unit. Hence, the configuration in which a predetermined clearance is provided between the second end of the high-voltage electrode and the surface on which the blowout outlet is formed prevents the direct discharge between the high-voltage electrode and the low-voltage electrode, and enables the discharge between the high-voltage electrode and the low-voltage electrode through the dielectric substrate, thereby preventing damage to the high-voltage electrode, dielectric substrate, and low-voltage electrode. Therefore, this configuration makes it possible to prevent the materials constituting these components from being mixed into the plasma as impurities.

In the above configuration, the portion of the dielectric substrate having a thickness being thinner when being closer to the blowout outlet may have a staircase shape.