PURPOSE: To easily obtain the desired quantity of ozone and to easily replace a wire rod even if it is exhausted by constituting an impressing electrode body of a rod and a wire rod which is attachably and detachably attached to the rod in the axial direction.

CONSTITUTION: A through hole 8 with the same diameter as the inside one of a pipe body 7 is pierced in a base 6. An impressing electrode rod is constituted of a cylindrical leg part 13 having a flange 12 at the lower end and a cylindrical impressing rod 14. When the leg part 13 and the impressing rod 14 are inserted into the pipe body 7 and through hole 8, a doughnut-shaped discharge gap of about 1mm width is formed to use them even with low impressing voltage. Plural grooves 16 are formed at equal intervals in the axial direction on the peripheral of the rod 14. A recessed part 17 is provided on the end surface of the rod 14 and notches are provided in the corresponding positions to the grooves 16 around the recessed part 17. Therefore, a tungsten wire 18 for an impressing electrode is put and turned along the grooves 16 and notches in the impressing rod 14 to obtain the desired length of the impressing electrode. A dielectric electrode body consists of a plate body 21 having square fins 4 and a heat sink end body 22.