PROBLEM TO BE SOLVED: To reduce running cost of using carbon dioxide gas in a plant cultivation facility such as a plant factory, greenhouse cultivation facility and the like.SOLUTION: An air supplying pipe 4 communicates between an office 1 and a plant cultivation facility 2. The air including carbon dioxide gas generated in the office 1 is transmitted from the office 1 to the plant cultivation facility 2 via the air supplying pipe 4 by virtue of a supplying pump 5 so as to utilize the air as carbon dioxide gas required for plant photosynthesis in the plant cultivation facility 2.