PURPOSE: To facilitate the impedance matching by adjusting a waveform generating line set at the rectangular wave pulse generating side to the load impedance that is not easily set.

CONSTITUTION: The equation I calculates the electrostatic capacity ΔC that is decided between a low voltage electrode 4 and a high voltage electrode 5 at each position of a 2nd dielectric 10 divided into (n) pieces. Therefore the impedance ΔZ1 is varied by the equation II when a drive mechanism 11 is actuated by (n) pieces of dielectric 10 and the capacity ΔC is varied. In other words, the impedance ΔZ1 can be easily changed with the change of the capacity ΔC since the inductance ΔL is decided by a structure regardless of the dielectric 10. The mechanism 11 can finely control the dielectric 10 by moving this dielectric up and down by a screw and the impedance ΔZ1 can also be continuously changed. Therefore the impedance ΔZ1 can always be matched with the impedance Z2 of the load 8 with the highly precise control of the dielectric 10.