A discharge reactor that generates silent discharge and/or creeping discharge between dielectric and high voltage electrode and/or grounded electrode, said dielectric being located between high voltage electrode and grounded electrode, and which generates clean ozone in the discharge space 1 as it passes through said discharge space 1 or as it is held within said discharge space 1, which discharge reactor is characterized in that the dielectric is made of highly purified quartz glass (SiO.sub.2) or single-crystal sapphire which is a highly purified crystallized aluminium oxide or high-purity alumina ceramics which is the firing of highly purified aluminum oxide. Further, in order to obtain cleaner and highly concentration ozone, at least the electrode or electrodes in the area of the discharge space which is to be exposed to discharge are made of a high-purity aluminum material and at least the area of the discharge space which is to be exposed to discharge is further coated with an anodic oxidation film.