An apparatus for producing high-concentration ozone gas has a plurality of adsorption/desorption columns and a plurality of valves capable of switching opening/closing of the passage of gas flowing into or out of the adsorption/desorption columns, such that each of the adsorption/desorption columns can performs ozone adsorption processing, evacuation processing or desorption processing. At least two of the adsorption/desorption columns are placed in a serial cycle arrangement to constitute a main adsorption/desorption column group, and one or more of the other adsorption/desorption columns is placed in parallel with the main adsorption/desorption column group to constitute an auxiliary adsorption/desorption column. The auxiliary adsorption/desorption column performs desorption processing during a period in which none of the adsorption/desorption columns of the main adsorption/desorption column group is performing desorption processing.