The low-voltage electrode 56 has a plate shape and is provided in the side facing the second surface 53b (the lower surface in FIG. 2) of the dielectric substrate 52. The low-voltage electrode 56 is formed with the groove 22 that is similar to that of the low-voltage electrode 20 according to the first embodiment. The groove 22 is formed with an inclined portion 56b having a thickness being thicker when being closer to the blowout outlet 30. As a result, the gas channel 25 includes a portion 58 in which a gap between the dielectric substrate 52 and the low-voltage electrode 56 becomes narrower when being closer to the blowout outlet 30. The second embodiment, which includes the portion in which the gap between the dielectric substrate 52 and the low-voltage electrode 56 becomes narrower when being closer to the blowout outlet 30, enables the amount of variation in capacitance to be further increased. In addition, including the portion in which the gap between the high-voltage electrode and the low-voltage electrode becomes narrower when being closer to the blowout outlet 30 enables the probability of discharge start to be improved. Since the discharge start voltage is proportional to the product of pressure and distance, the discharge will start near a tip where the distance between the high-voltage electrode and the low-voltage electrode is close in the initial start, and the discharge will subsequently spread to the area with a thicker dielectric layer in the rear part. Including the portion in which the gap between the dielectric substrate 52 and the low-voltage electrode 56 becomes narrower when being closer to the blowout outlet 30 enables the plasma generator to be reliably started and discharged stably. Including the portion in which the distance between the high-voltage electrode and the low-voltage electrode is close along the longitudinal direction of the blowout outlet allows plasma to be generated evenly near the tip of the blowout outlet even when the plasma discharge is performed at low power, enabling uniform processing. Therefore, this configuration is capable of adjusting the power input to the plasma generator, expanding the range of plasma processing applications.