A container refrigeration apparatus which includes a refrigerant circuit performing a refrigeration cycle, and which is attached to a container that stores plants to cool air in the interior of the container, the container refrigeration apparatus comprising: an oxygen concentration detector which detects an oxygen concentration in the interior of the container; and a gas mixture supplier which supplies the interior of the container with a gas mixture having a higher nitrogen concentration and a lower oxygen concentration than outside air, where the oxygen concentration of the gas mixture is higher than a predetermined target concentration, wherein the gas mixture supply device is configured to: reduce the oxygen concentration in the interior of the container to the vicinity of the oxygen concentration of the gas mixture by supplying the interior of the container with the gas mixture if the oxygen concentration detected by the oxygen concentration detector is higher than the oxygen concentration of the gas mixture; stop supplying the gas mixture since the oxygen concentration in the interior of the container has been reduced to the vicinity of the oxygen concentration of the gas mixture and until the oxygen concentration in the interior of the container is reduced to the target concentration by respiration of the plants absorbing oxygen in the air and releasing carbon dioxide into the air; and increase the oxygen concentration in the interior of the container to the target concentration by supplying the interior of the container with the gas mixture if the oxygen concentration detected by the oxygen concentration detector is lower than the target concentration. an oxygen concentration detector which detects an oxygen concentration in the interior of the container; and a gas mixture supplier which supplies the interior of the container with a gas mixture having a higher nitrogen concentration and a lower oxygen concentration than outside air, where the oxygen concentration of the gas mixture is higher than a predetermined target concentration, wherein the gas mixture supply device is configured to: reduce the oxygen concentration in the interior of the container to the vicinity of the oxygen concentration of the gas mixture by supplying the interior of the container with the gas mixture if the oxygen concentration detected by the oxygen concentration detector is higher than the oxygen concentration of the gas mixture; stop supplying the gas mixture since the oxygen concentration in the interior of the container has been reduced to the vicinity of the oxygen concentration of the gas mixture and until the oxygen concentration in the interior of the container is reduced to the target concentration by respiration of the plants absorbing oxygen in the air and releasing carbon dioxide into the air; and increase the oxygen concentration in the interior of the container to the target concentration by supplying the interior of the container with the gas mixture if the oxygen concentration detected by the oxygen concentration detector is lower than the target concentration. reduce the oxygen concentration in the interior of the container to the vicinity of the oxygen concentration of the gas mixture by supplying the interior of the container with the gas mixture if the oxygen concentration detected by the oxygen concentration detector is higher than the oxygen concentration of the gas mixture; stop supplying the gas mixture since the oxygen concentration in the interior of the container has been reduced to the vicinity of the oxygen concentration of the gas mixture and until the oxygen concentration in the interior of the container is reduced to the target concentration by respiration of the plants absorbing oxygen in the air and releasing carbon dioxide into the air; and increase the oxygen concentration in the interior of the container to the target concentration by supplying the interior of the container with the gas mixture if the oxygen concentration detected by the oxygen concentration detector is lower than the target concentration.