Abstract: A cylindrical tank-shaped container including: plural parallel electrode tubes; discharge tubes arranged inside the electrode tubes, each forming a discharge gap; a pair of end plates that penetrate and hold both of end sections of the plural electrode tubes; a cooling space formed by the pair of end plates and the inner surface of the tank-shaped container divided between end plates; a cooling medium inlet and a cooling medium outlet formed in opposite end sides of the cooling space; a raw material gas inlet that introduces raw material gas to be sent to the discharge gaps; and an outlet for ozone gas generated from the raw material gas by silent discharge in the discharge gaps, providing an electrode tube in which a discharge tube is not arranged, among the plural electrode tubes, that have surrounding coolant medium that reaches at least a prescribed temperature resulting from the silent discharge.