Patent attributes
An oxygen concentration in the interior of a container is detected by an oxygen concentration detection sensor. If the oxygen concentration detected by the oxygen concentration detection sensor is higher than that of a gas mixture, the container is supplied with the gas mixture having an oxygen concentration lower than that of the outside air and higher than a target concentration. The oxygen concentration in the interior of the container is reduced to the vicinity of the oxygen concentration of the gas mixture by supplying the interior of the container with the gas mixture, and then is further reduced to the target concentration by respiration of plants. This appropriately controls the oxygen concentration in the interior of the container, and reduces a decrease in the degree of freshness of the plants.
