PURPOSE: To form a large amt. of ozone by generating the creeping discharge elongating between counter electrodes with a relatively low impressed voltage.

CONSTITUTION: A thin dielectric plate 5 for preventing shorting is provided between the electrodes 1 and 2 facing each other and many supporting dielectric plates 31, 32 are disposed respectively symmetrically with the dielectric plate between this dielectric plate and the electrodes to support the electrodes facing each other in parallel and the provide slopes in the contact parts of the supporting dielectric substances with the electrode surfaces so as to sharpen the angle formed by the electrode surface and the supporting dielectric substance surface, by which the creeping corona discharge is more easily generated. The creeping corona elongates to the counter electrode side but the shorting thereof is prevented by the dielectric plate for preventing shorting and, therefore, the impressed voltage is increased and the creeping corona is increased. A large amt. of ozone is thus generated.