In the present invention, a CA device (60) comprises: a gas supply device (30) that performs a gas supply operation for supplying low-oxygen-concentration air into a container (11)； and a controller (55) that controls the operation of the gas supply device (30) so as to achieve a desired composition for the air inside the container. The controller (55) is configured to be capable of executing a carbon dioxide concentration adjustment operation in which the controller adjusts the composition of the air inside the container to a desired composition, if the oxygen concentration of the air inside the container is greater than a target oxygen concentration, by causing the gas supply device (30) to perform the gas supply operation while changing the amount of gas supplied, such that the carbon dioxide concentration of the air inside the container falls within a prescribed reference concentration range.
