Disclosed herein is a CA system (60) which allows first and second adsorption columns (34, 35) 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 (11). The CA system (60) 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 (11), and the nitrogen-enriched air produced until the end of the desorption operation since the predetermined time passed is supplied into the container (11).
