PROBLEM TO BE SOLVED: To provide a COgas concentration device which can concentrate COgas in the outside air and efficiently supply it to a plant factory or a greenhouse for gardening, and for which device cost can be suppressed low and an electricity rate and running cost for maintenance can be also reduced, and a COgas concentration method using the device.SOLUTION: A COconcentration device comprises: a first pressure container 1 for concentrating COgas; a second pressure container 2 for storing air which is connected to the first pressure container; and an energy recovery-type air compressor 3 which is arranged between the first pressure container 1 and a plant cultivation chamber R, has a built-in electric motor M as a driving source, and can feed the outside air under pressure from an air intake part 31 to the first pressure container 1 and the second pressure container 2, and in which the electric motor M works as a generator G when compressed gas stored in each of the pressure containers 1 and 2 is tra
