The ozonizer of this present invention is small in size, and capable of generating highly concentrated ozone with a high (generating) efficiency. A low voltage electrode includes a disc-shaped low voltage electrode main body facing a high voltage electrode and an extension at one side of the low voltage electrode main body, and the extensions are laminated in layers on a base via blocks, and a coolant inlet portion for supplying coolant to a coolant passage, a coolant outlet portion for exhausting coolant from the coolant passage, and an ozone gas outlet portion for exhausting ozone gas from the ozone gas passage pass through the extensions and the blocks, respectively, in a laminating direction of the discharge cells.