Provided is an ozone concentrator including an ozone generator (3), adsorption/desorption columns (4) in which silica gel (6) cooled with a certain-temperature refrigerant (25) for concentrating ozone generated by the ozone generator (3) is packed, a refrigerating machine (23) for cooling the refrigerant (25), a vacuum pump (20) for enhancing a concentration of the ozone in one of the adsorption/desorption columns (4) by discharging mainly oxygen from the silica gel (6) adsorbing the ozone, a plurality of valves (8) to (13) for air pressure operations, for switching passages of gas that is allowed to flow in or flow out with respect to the adsorption/desorption columns (4), and ozone concentration meters (28, 29) for measuring the concentration of the ozone enhanced by the vacuum pump (20), in which a discharge line of the vacuum pump (20) is connected to another one of the adsorption/desorption columns (4), whereby the ozone is allowed to pass through another one of the adsorption/desorption columns again. Therefore, stable ozone of high concentration can be generated at a satisfactory energy efficiency without any temperature difference between upper and lower positions of adsorption/desorption columns.