Abstract: An ozone generator is formed by a plurality of concentric tubular plate members forming positive and negative electrodes which are interleaved with each other. A high voltage discharge is applied from a transformer between the electrodes to cause an electric discharge in the air contained therebetween, thereby generating a supply of ozone. The air is fed to a suction nozzle device through which a water stream to be purified passes. The suction nozzle is constructed so that the water stream is markedly speeded up so as to generate a partial vacuum in an air pocket formed between the water stream and the inner walls of the nozzle. The ozone, which is fed to the nozzle in the region where this air pocket is formed, is thus sucked into the nozzle and efficiently injected into the water stream, thereby effecting the purifying action.