Disclosed herein is a CA system which allows first and second adsorption columns to alternately perform an adsorption operation and a desorption operation so that nitrogen-enriched air having a higher nitrogen concentration and a lower oxygen concentration than the air is produced and supplied into the container. The CA system executes a second operation mode in which the nitrogen-enriched air produced for a predetermined time since the desorption operation was started is discharged to the outside of the container, and the nitrogen-enriched air produced until the end of the desorption operation since the predetermined time passed is supplied into the container.
